Add "-h/-H" parsing to "git grep"

Add "-h/-H" parsing to "git grep"

It turns out that I actually wanted to avoid the filenames (because I
didn't care - I just wanted to see the context in which something was
used) when doing a grep. But since "git grep" didn't take the "-h"
parameter, I ended up having to do "grep -5 -h *.c" instead.

So here's a trivial patch that adds "-h" (and thus has to enable -H too)
to "git grep" parsing.

Signed-off-by: Linus Torvalds <redacted>
Signed-off-by: Junio C Hamano <redacted>