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>

hash-object.c

@@ -110,7 +110,7 @@ int main(int argc, const char **argv)
 	}
 
 	if (errstr) {
-		error (errstr);
+		error("%s", errstr);
 		usage_with_options(hash_object_usage, hash_object_options);
 	}