commit-tree: update the command line parsing

We have kept the original "git commit-tree <tree> -p <parent> ..." syntax
forever, but "git commit-tree -p <parent> -p <parent> ... <tree>" would be
more intuitive way to spell it. Dashed flags along with their arguments
come first and then the "thing" argument after the flags.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit-tree.c

@@ -27,7 +27,7 @@ static void new_parent(struct commit *parent, struct commit_list **parents_p)
 
 int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 {
-	int i;
+	int i, got_tree = 0;
 	struct commit_list *parents = NULL;
 	unsigned char tree_sha1[20];
 	unsigned char commit_sha1[20];
@@ -37,20 +37,25 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 
 	if (argc < 2 || !strcmp(argv[1], "-h"))
 		usage(commit_tree_usage);
-	if (get_sha1(argv[1], tree_sha1))
-		die("Not a valid object name %s", argv[1]);
 
-	for (i = 2; i < argc; i += 2) {
-		unsigned char sha1[20];
-		const char *a, *b;
-		a = argv[i]; b = argv[i+1];
-		if (!b || strcmp(a, "-p"))
-			usage(commit_tree_usage);
+	for (i = 1; i < argc; i++) {
+		const char *arg = argv[i];
+		if (!strcmp(arg, "-p")) {
+			unsigned char sha1[20];
+			if (argc <= ++i)
+				usage(commit_tree_usage);
+			if (get_sha1(argv[i], sha1))
+				die("Not a valid object name %s", argv[i]);
+			assert_sha1_type(sha1, OBJ_COMMIT);
+			new_parent(lookup_commit(sha1), &parents);
+			continue;
+		}
 
-		if (get_sha1(b, sha1))
-			die("Not a valid object name %s", b);
-		assert_sha1_type(sha1, OBJ_COMMIT);
-		new_parent(lookup_commit(sha1), &parents);
+		if (get_sha1(arg, tree_sha1))
+			die("Not a valid object name %s", arg);
+		if (got_tree)
+			die("Cannot give more than one trees");
+		got_tree = 1;
 	}
 
 	if (strbuf_read(&buffer, 0, 0) < 0)