Prefer younger merge bases over older ones.

git-core prefers younger merge bases over older ones in case that multiple valid merge bases exists.

src/commit_list.c

@@ -36,7 +36,7 @@ git_commit_list *git_commit_list_insert_by_date(git_commit_list_node *item, git_
 	git_commit_list *p;
 
 	while ((p = *pp) != NULL) {
-		if (git_commit_list_time_cmp(p->item, item) < 0)
+		if (git_commit_list_time_cmp(p->item, item) > 0)
 			break;
 
 		pp = &p->next;