Allow in_merge_bases() to take more than one reference commits.

The internal function in_merge_bases(A, B) is used to make sure
that commit A is an ancestor of commit B.  This changes the
signature of it to take an array of B's and updates its current
callers.

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

commit.h

@@ -114,5 +114,5 @@ extern int is_repository_shallow();
 extern struct commit_list *get_shallow_commits(struct object_array *heads,
 		int depth, int shallow_flag, int not_shallow_flag);
 
-int in_merge_bases(struct commit *rev1, struct commit *rev2);
+int in_merge_bases(struct commit *, struct commit **, int);
 #endif /* COMMIT_H */