More changes in the Emacs manual

More changes in the Emacs manual

* doc/emacs/search.texi (Regexp Backslash): Say that
symbol-constituent characters are determined by the syntax table.
(Lax Search): Fix example of case-insensitive search.  Fix a
typo.
(Unconditional Replace): Improve wording.
(Regexp Replace): More consistent wording.  Reported by Michael
Albinus <michael.albinus@gmx.de> in emacs-manual-bugs@gnu.org.

* doc/emacs/msdos.texi (Windows HOME): Avoid enumerating all the
Windows versions.  Reported by Isaac Carter
<icarter1391@gmail.com> in emacs-manual-bugs@gnu.org.