bug#18837: 25.0.50; `sort` -- modify function to preserve original list.

[Keith David Bershatsky]

The doc-string for the function `sort` states that `SEQ is modified by side 
effects`; however, it does not state in what way the original list gets 
modified or why such a feature might somehow be useful.  I attempted to find 
out the answer to this question on `superuser.com`, however, the community has 
expressed an interest in closing the question without offering an explanation 
on this issue:

http://superuser.com/questions/831608/emacs-sort-usefulness-of-side-effect-modifying-initial-list

In my use case, I want to preserve an initial list that is set to a let-bound 
variable so that I can use it again elsewhere in the function.  To achieve this 
objection, I used `copy-list`.

Unless the modified `SEQ` is somehow useful, perhaps it would be appropriate to 
modify the function `sort` so that it preserves the initial list.

Thanks,

Keith

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

In GNU Emacs 25.0.50.1 (x86_64-apple-darwin10.8.0, NS appkit-1038.36 Version 
10.6.8 (Build 10K549))
 of 2014-10-01 on MP.local
Repository revision: 117996 dmantipov@yandex.ru-20141001132108-zdsxru2390mqyjlu
Windowing system distributor `Apple', version 10.3.1038
Configured using:
 `configure --with-ns'

Configured features:
ACL LIBXML2 ZLIB

Important settings:
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  sd-mode: t
  sb-mode: t
  tb-mode: t
  shell-dirtrack-mode: t
  cm-mode: t
  bc-mode: t
  as-mode: t
  ds-mode: t
  ml-mode: t

Recent input:

Recent messages:

Load-path shadows:
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/md4 hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/md4
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/hex-util hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/hex-util
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/sasl hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/net/sasl
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/sasl-ntlm hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/net/sasl-ntlm
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/sasl-digest hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/net/sasl-digest
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/sasl-cram hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/net/sasl-cram
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/ntlm hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/net/ntlm
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/hmac-md5 hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/net/hmac-md5
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/hmac-def hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/net/hmac-def
/Users/HOME/.0.data/.0.emacs/.0.wl/rfc2368 hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/mail/rfc2368
/Users/HOME/.0.data/.0.emacs/.0.wl/utf7 hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/gnus/utf7
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/smime hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/gnus/smime
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/pgg hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/obsolete/pgg
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/pgg-pgp5 hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/obsolete/pgg-pgp5
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/pgg-pgp hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/obsolete/pgg-pgp
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/pgg-parse hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/obsolete/pgg-parse
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/pgg-gpg hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/obsolete/pgg-gpg
/Users/HOME/.0.data/.0.emacs/.0.apel_flim_simi/pgg-def hides 
/Users/HOME/.0.data/.0.emacs/Emacs_10_01_2014.app/Contents/Resources/lisp/obsolete/pgg-def

Features:
(shadow mime-setup mail-mime-setup semi-setup mime-image modb-standard
elmo-imap4 mule-util eieio-opt speedbar sb-image ezimage dframe
emacsbug lawlist-desktop frameset lawlist-colors reporter lawlist-dv
lawlist-mc rect lawlist-ztree lawlist-wl elmo-nntp wl-demo wl-news
wl-address wl-thread wl wl-e21 wl-draft elmo-pop3 wl-template elmo-net
elmo-cache elmo-map elmo-dop wl-folder wl-spam wl-action wl-summary
wl-refile wl-message wl-mime pgg mime-pgp wl-util pp elmo-flag
elmo-localdir mime-play filename mime-edit eword-encode pgg-parse pccl
pccl-20 pgg-def signature sendmail elmo-mime mmelmo-buffer mmelmo-imap
mime-view mime-conf calist semi-def mmimap mime-parse mmbuffer
mmgeneric elmo-filter elmo-multi elmo-spam elsp-header elsp-generic
elmo elmo-signal wl-highlight wl-vars wl-version elmo-msgdb modb
modb-generic modb-entity luna mime elmo-util emu invisible inv-23 poem
poem-e20 poem-e20_3 eword-decode std11 elmo-date elmo-vars
elmo-version w3m-load mime-w3m w3m browse-url doc-view jka-compr
image-mode w3m-hist w3m-fb bookmark-w3m w3m-ems w3m-ccl ccl
w3m-favicon w3m-image w3m-proc w3m-util lawlist-dired dired-aux
lawlist-vr-hr lawlist-ws disp-table lawlist-calc lawlist-flyspell
lawlist-yas lawlist-tex-mode skeleton compare-w lawlist-txt-mode
lawlist-tabbar lawlist-github ido view vc-git vc vc-dispatcher tramp
tramp-compat tramp-loaddefs trampver shell thingatpt time-stamp rx
log-view log-edit pcvs-util add-log help-mode grep compile find-lisp
epa epg epg-config ediff-merg ediff-wind ediff-diff ediff-mult
ediff-help ediff-init ediff-util ediff ert ewoc debug eieio-base
diff-mode conf-mode autorevert filenotify lorg-calendar org-element
lorg-search org-agenda context-menu dired-read-filename
lawlist-toodledo url-http url-auth url-gw url url-proxy url-privacy
url-expand url-methods url-history url-cookie url-domsuf url-util
url-parse auth-source eieio eieio-core password-cache url-vars mailcap
json xml lawlist-org lawlist-calendar derived org byte-opt bytecomp
byte-compile cconv org-macro org-footnote org-pcomplete pcomplete
org-list org-faces org-entities org-version ob-emacs-lisp ob ob-tangle
org-src ob-ref ob-lob ob-table ob-keys ob-exp ob-comint comint
ansi-color ring ob-core ob-eval org-compat org-macs org-loaddefs
cal-menu calendar cal-loaddefs noutline outline gnus-sum gnus-group
gnus-undo gnus-start gnus-cloud nnimap nnmail mail-source tls utf7 mel
path-util mime-def alist mcharset mcs-20 mcs-e20 pcustom pces pces-e20
pces-20 broken poe pym static apel-ver product netrc nnoo parse-time
gnus-spec gnus-int gnus-range message dired format-spec mml mml-sec
mm-decode mm-bodies mm-encode gmm-utils mailheader gnus-win
lawlist-frame lawlist-cm lawlist-bbdb gnus gnus-ems nnheader gnus-util
mail-utils wid-edit mail-parse rfc2231 rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mailabbrev mail-extr rfc822 cl timezone
lawlist-init pcase cl-macs gv advice help-fns easy-mmode edmacro
kmacro cl-loaddefs cl-lib savehist server ps-print ps-def lpr
find-func saveplace easymenu time-date tooltip electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel ns-win tool-bar dnd fontset
image regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
minibuffer nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
cocoa ns multi-tty emacs)

Memory information:
((conses 16 1096676 58375)
 (symbols 48 62784 0)
 (miscs 40 214 364)
 (strings 32 147723 21599)
 (string-bytes 1 4679349)
 (vectors 16 42737)
 (vector-slots 8 761520 19326)
 (floats 8 1105 51)
 (intervals 56 5302 730)
 (buffers 976 15))