bug#23417: 25.1.50; Elisp manual: document gotcha about new objects and quoting

[Drew Adams]

In the Elisp manual, we do, in node `Rearrangement', point out the
gotcha that a quoted list sexp does not necessarily return a new list
(new cons) each time it occurs in code.

However:

1. The gotcha is more general than the nconc context where it is
presented.  It is not limited to using a quoted constant list as a
non-last arg to nconc.

2. The gotcha is not limited to quoted constant lists.  It applies
to #s also.

3. Please consider presenting the gotcha in general terms, somewhere.
And that place can then be cross-referenced from relevant nodes (e.g.
`Quoting' and `Creating Hash').

4. Please correct misleading text, such as this from `Creating Hash',
so as not to give the impression that you get a new object for each
occurrence of a quoted constant.

   You can also create a new hash table using the printed
   representation for hash tables.

Here is one example of confusion wrt the gotcha for #s:
http://stackoverflow.com/q/36964728/729907


In GNU Emacs 25.1.50.1 (i686-pc-mingw32)
 of 2015-12-10
Repository revision: 6148555ee5a3d0139ae517803718b3e0357933c7
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/snapshot/trunk --enable-checking=yes
 --enable-check-lisp-object-type --without-compress-install 'CFLAGS=-Og
 -ggdb3' LDFLAGS=-Lc:/Devel/emacs/lib 'CPPFLAGS=-DGC_MCHECK=1
 -Ic:/Devel/emacs/include''