grep.[ch]: extend grep_opt to allow showing matched column

grep.[ch]: extend grep_opt to allow showing matched column

To support showing the matched column when calling 'git-grep(1)', teach
'grep_opt' the normal set of options to configure the default behavior
and colorization of this feature.

Now that we have opt->columnnum, use it to disable short-circuiting over
ORs and ANDs so that col and icol are always filled with the earliest
matches on each line. In addition, don't return the first match from
match_line(), for the same reason.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>