Fix the build of the Emacs User manual.

 doc/emacs/maintaining.texi (Version Control Systems): Move "@end itemize"
 past the last @item.  Fix a typo (reported by H. Dieter Wilhelm
 <dieter@duenenhof-wilhelm.de>).
Fix bug #1702 with missing feature in arc-mode.el.

 lisp/arc-mode.el (archive-visit-single-files): New.
 (archive-mode): Visit file if archive contains a single file.
Fix bug #19084 with 'C-x v +' in *vc-change-log* buffers.

 lisp/vc/vc.el (vc-deduce-fileset): Support invocation from
 *vc-change-log* buffer.