Add '--bisect' revision machinery argument

I personally use "git bisect visualize" all the time when I bisect, but it
turns out that that is not a very flexible model. Sometimes I want to do
bisection based on all commits (no pathname limiting), but then visualize
the current bisection tree with just a few pathnames because I _suspect_
those pathnames are involved in the problem but am not totally sure about
them.

And at other times, I want to use other revision parsing logic, none of
which is available with "git bisect visualize".

So this adds "--bisect" as a revision parsing argument, and as a result it
just works with all the normal logging tools. So now I can just do

	gitk --bisect --simplify-by-decoration filename-here

etc.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.h

@@ -63,6 +63,7 @@ struct rev_info {
 			reverse:1,
 			reverse_output_stage:1,
 			cherry_pick:1,
+			bisect:1,
 			first_parent_only:1;
 
 	/* Diff flags */