bug#23937: 25.0.95; Search functions doc fixes/improvements

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: Stephen Berman <stephen.berman@gmx.net>,  23937@debbugs.gnu.org
> Date: Tue, 12 Jul 2016 17:14:19 +0200
> 
>    With COUNT positive, the match found is the COUNTth to last one (or
>      last, if COUNT is 1 or nil) in the buffer located entirely before
>      the origin of the search; correspondingly with COUNT negative.

OK.