Support "git cmd --help" syntax

Support "git cmd --help" syntax

The "--help" argument is special, in that it is (along with "--version")
in that is taken by the "git" program itself rather than the sub-command,
and thus we've had the syntax "git --help cmd".

However, as anybody who has ever used CVS or some similar devil-spawn
program, it's confusing as h*ll when options before the sub-command act
differently from options after the sub-command, so this quick hack just
makes it acceptable to do "git cmd --help" instead, and get the exact same
result.

It may be hacky, but it's simple and does the trick.

Of course, this does not help if you use one of the non-builtin commands
without using the "git" helper. Ie you won't be getting a man-page just
because you do "git-rev-list --help". Don't expect us to be quite _that_
helpful.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>