git-log --first-parent: show only the first parent log

If your development history does not have fast-forward merges,
i.e. the "first parent" of commits in your history are special
than other parents, this option gives a better overview of the
evolution of a particular branch.

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

revision.h

@@ -46,7 +46,8 @@ struct rev_info {
 			boundary:2,
 			left_right:1,
 			parents:1,
-			reverse:1;
+			reverse:1,
+			first_parent_only:1;
 
 	/* Diff flags */
 	unsigned int	diff:1,