git-rev-parse: pass on "--" flag when required

git-rev-parse: pass on "--" flag when required

If rev-parse output includes both flags and files, we should pass on any
"--" marker we see, so that the end result can also tell the difference
between a flag and a filename that begins with '-'.

[jc: merged a later one liner updates from Linus]

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