bug#28070: 24.5; doc string of `eval-buffer'

[Drew Adams]

The doc string should, like Elisp manual node `Eval', mention that this
does NOT always "Execute the current buffer as Lisp code."  It acts on the 
current buffer restriction, if any.

As the manual says:

  `eval-buffer' operates on the entire accessible portion of buffer
                                       ^^^^^^^^^^^^^^^^^^

That qualification changes everything.  We don't always need to point
out explicitly that a particular function acts on the accessible portion
of the buffer, but it is important to do so in this case.

In GNU Emacs 24.5.1 (i686-pc-mingw32)
 of 2015-04-11 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=3D/c/usr --host=3Di686-pc-mingw32'