Move "--parent" parsing into generic revision.c library code

Not only do we do it in both rev-list.c and git.c, the revision walking
code will soon want to know whether we should rewrite parenthood
information or not.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

revision.h

@@ -34,7 +34,8 @@ struct rev_info {
 			edge_hint:1,
 			limited:1,
 			unpacked:1,
-			boundary:1;
+			boundary:1,
+			parents:1;
 
 	/* special limits */
 	int max_count;