bug#21225: 25.0.50; doc strings of `define-obsolete-*'

[Drew Adams]

Argument WHEN is not described at all for some of these macros.  For
others it is described incorrectly or only via an example.  It needs to
be described clearly.

The correct description is, in all cases, what is said in the Elisp
manual for `make-obsolete':

   If provided, WHEN should be a string indicating when the function
   was first made obsolete=81\for example, a date or a release number.

(with "function" replaced by "face" or "variable", as appropriate),
except that "version number" is preferable to "release number".

These macros are used by users and 3rd-party libraries too, not just by
core Emacs development, and in such contexts "release" is not
necessarily appropriate.  The most important remark, however, is that "a
date" should be offered as an example of a WHEN value, in addition to "a
version number".

The same change should be made for the Elisp manual, node `Variable
Aliases'.  It is better to say "for example, a date or a version number"
than just "(usually a version number string)".

In GNU Emacs 25.0.50.1 (i686-pc-mingw32)
 of 2015-07-03 on LEG570
Repository revision: 2b848fadd51e805b2f46da64c5958ea7f009048a
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --host=3Di686-pc-mingw32 --enable-checking=3Dyes,glyphs'