branch: give better message when no names specified for rename

Signed-off-by: Jonathon Mah <me@JonathonMah.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -880,7 +880,9 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		if (edit_branch_description(branch_name))
 			return 1;
 	} else if (rename) {
-		if (argc == 1)
+		if (!argc)
+			die(_("branch name required"));
+		else if (argc == 1)
 			rename_branch(head, argv[0], rename > 1);
 		else if (argc == 2)
 			rename_branch(argv[0], argv[1], rename > 1);

t/t3200-branch.sh

@@ -78,7 +78,7 @@ test_expect_success \
 test_expect_success \
     'git branch -m dumps usage' \
        'test_expect_code 128 git branch -m 2>err &&
-	test_i18ngrep "too many branches for a rename operation" err'
+	test_i18ngrep "branch name required" err'
 
 test_expect_success \
     'git branch -m m m/m should work' \