Fold get_merge_bases_clean() into get_merge_bases()

Change get_merge_bases() to be able to clean up after itself if
needed by adding a cleanup parameter.

We don't need to save the flags and restore them afterwards anymore;
that was a leftover from before the flags were moved out of the
range used in revision.c.  clear_commit_marks() sets them to zero,
which is enough.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/merge-base.c b/merge-base.c
index b41f76c..59f723f 100644
--- a/merge-base.c
+++ b/merge-base.c
@@ -6,7 +6,7 @@
 
 static int merge_base(struct commit *rev1, struct commit *rev2)
 {
-	struct commit_list *result = get_merge_bases(rev1, rev2);
+	struct commit_list *result = get_merge_bases(rev1, rev2, 0);
 
 	if (!result)
 		return 1;