This lets you say:

	git grep --all-match -e A -e B -e C

to find lines that match A or B or C but limit the matches from
the files that have all of A, B and C.

This is different from

	git grep -e A --and -e B --and -e C

in that the latter looks for a single line that has all of these
at the same time.

Signed-off-by: Junio C Hamano <junkio@cox.net>