More fixes for the Emacs manual

More fixes for the Emacs manual

* doc/emacs/vc1-xtra.texi (Customizing VC): Update the list of
backends.
* doc/emacs/maintaining.texi (Version Control): Add SRC to the
list of VCS.  Remove the description of vc-state-refresh.
(Version Control Systems): Update the description of CVS.
(VC Change Log): Amend the list of VCS that don't support
vc0print-root-log.
(VCS Changesets, VCS Repositories, Advanced C-x v v)
(VC Change Log): Mention SRC with RCS where appropriate.
(VC Directory Commands): More accurate description of
vc-dir-hide-up-to-date.  Suggested by Michael Albinus
<michael.albinus@gmx.de> in emacs-manual-bugs@gnu.org.