bug#20470: 24.5; VC log buffer no longer scrolls itself

[Raoul Gough]

How to reproduce: open a file checked out from RCS, hit C-x v l (or
equivalently M-x vc-print-log RET) and notice that the cursor ends up at
the start of the *vc-change-log* buffer. It should jump to the log
message for the current revision, which was the case until the fix for
bug #15322 "VC log buffer scrolls itself"

Clearly some people don't like the original feature, so I propose that
this feature be made optional instead of unconditionally disabled.

The particular revision control system doesn't really matter, I picked
RCS because it's minimal. If you don't have a file in RCS already, but
have RCS tools installed and a UNIX-like shell, you can do the
following:

$ touch foo
$ ci -l -t-foo foo
$ emacs foo
(then proceed with the C-x v l)



In GNU Emacs 24.5.1 (i686-apple-darwin, NS apple-appkit-1038.36)
 of 2015-04-10 on builder10-6.porkrind.org
Windowing system distributor `Apple', version 10.3.1038
Configured using:
 `configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --host=i686-apple-darwin
 --build=i686-apple-darwin --with-jpeg=no --with-png=no --with-gif=no
 --with-tiff=no'

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

Major mode: Log-View

Minor modes in effect:
  iswitchb-mode: t
  delete-selection-mode: t
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Type C-x 1 to delete the help window.
Quit
Setting up indent for shell type sh
Indentation variables are now local.
Indentation setup for shell type sh
Mark set [2 times]
Beginning of buffer [5 times]
End of buffer [2 times]
Beginning of buffer [4 times]
<A-C-M-drag-n-drop> is undefined

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils log-view easy-mmode pcvs-util vc vc-dispatcher
vc-rcs sh-script smie executable help-mode help-fns edmacro kmacro
iswitchb delsel python easymenu json comint ansi-color ring desktop
frameset cl-loaddefs cl-lib rmg-utils 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 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 8 91293 3952)
 (symbols 24 19601 0)
 (miscs 20 109 177)
 (strings 16 17438 3541)
 (string-bytes 1 507342)
 (vectors 8 12412)
 (vector-slots 4 421722 3144)
 (floats 8 62 522)
 (intervals 28 278 6)
 (buffers 512 15))