Fix non-literal format in printf-style calls

These were found using gcc 4.3.2-1ubuntu11 with the warning:

    warning: format not a string literal and no format arguments

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

builtin-check-attr.c

@@ -97,7 +97,7 @@ int cmd_check_attr(int argc, const char **argv, const char *prefix)
 	else if (stdin_paths && doubledash < argc)
 		errstr = "Can't specify files with --stdin";
 	if (errstr) {
-		error (errstr);
+		error("%s", errstr);
 		usage_with_options(check_attr_usage, check_attr_options);
 	}