* .gitignore: Add /emacs-[1-9]*/, and sort better.
Fix VC documentation related to switching branches.

 lisp/vc/vc.el (vc-retrieve-tag): Doc fix.

 doc/emacs/maintaining.texi (Switching Branches): Mention "C-x v r".
 Correct commands for switching branches in various VCSs.
.gitignore: Resurrect Windows-specific ignorables lost in last changes.