git-mv: Allow -h without repo & fix error message
git-mv: Allow -h without repo & fix error message

This fixes "git-mv -h" to output the usage without the need
to be in a git repository.
Additionally:
- fix confusing error message when only one arg was given
- fix typo in error message

Signed-off-by: Josef Weidendorfer <cd09c6f9ce317d005f2d2d124e6e1764b163fdc4@gmx.de>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git