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>