bug#15343: 24.3.50; Document window point better in Emacs manual

[Drew Adams <drew.adams@oracle.com>]

The concept of point is fundamental to Emacs, and it is introduced in
(emacs) `Point'.  However, users sometimes get confused because multiple
windows for the same buffer have different notions of point: the window
point.  This concept is hardly presented in the Emacs manual, AFAICT.
The most that is said is this, which is easily missed in (emacs)
`Point':

 Furthermore, if a buffer is displayed in multiple windows, each of
 those windows has its own value of point.

Great, but what are the consequences of that?  In particular, what are
some gotchas that might confuse users?

I don't have a great suggestion of what the improvement might be, but I
think something more is needed to dispel or prevent this confusion.
Perhaps an example, to illustrate the notion and the possible confusion.

This problem report comes to mind in this regard.  Dunno whether the
problem reported here is really due to confusion about `window-point',
but I can see such a problem possibly coming from such confusion.

http://stackoverflow.com/questions/18734850/point-moves-when-switching-buffers-in-emacs-aquamacs/18744622#18744622



In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-08-31 on ODIEONE
Bzr revision: 114088 rgm@gnu.org-20130901021232-sazo0qla2qgcko95
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3' LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'