bug#15117: 24.3.50; doc of `(forward|backward)-*': state return value

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

These are motion functions, just like `goto-char' and
`skip-chars-forward'.  Their doc should specify the return value
(regardless of whether it is a position, a Boolean, always nil, or
anything else).

If, for some special (good) reason, code should not rely on the return
value of some function then this fact should be stated explicitly in
the doc: "This function is used only for its side effects; the return
value is undefined."  This is Lisp, not C - return values are the norm,
not the exception.

The doc of `(forward|backward)-(word|line)' already correctly specifies
the return value.  Not so for other `(forward|backward)-*' functions,
such as `(forward|backward)-sexp'.


In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-08-07 on ODIEONE
Bzr revision: 113750 lekktu@gmail.com-20130808011911-0jzpc9xuncegg6x9
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'