merge: simplify merge_trivial() by using commit_list_append()

Build the commit_list of parents by calling commit_list_append() twice
instead of allocating and linking the items by hand.  This makes the
code shorter and simpler.  Rename the commit_list from parent to parents
(plural) while at it because there are two of them.
Signed-off-by: NRene Scharfe <l.s.r@web.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/merge.c

@@ -843,16 +843,14 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 {
 	unsigned char result_tree[20], result_commit[20];
-	struct commit_list *parent = xmalloc(sizeof(*parent));
+	struct commit_list *parents, **pptr = &parents;
 
 	write_tree_trivial(result_tree);
 	printf(_("Wonderful.\n"));
-	parent->item = head;
-	parent->next = xmalloc(sizeof(*parent->next));
-	parent->next->item = remoteheads->item;
-	parent->next->next = NULL;
+	pptr = commit_list_append(head, pptr);
+	pptr = commit_list_append(remoteheads->item, pptr);
 	prepare_to_commit(remoteheads);
-	if (commit_tree(merge_msg.buf, merge_msg.len, result_tree, parent,
+	if (commit_tree(merge_msg.buf, merge_msg.len, result_tree, parents,
 			result_commit, NULL, sign_commit))
 		die(_("failed to write commit object"));
 	finish(head, remoteheads, result_commit, "In-index merge");