change uid/gid fields in mail_user from unsigned to signed

(in incremental sql-files this was already done in upd_0064.sql)

install/sql/ispconfig3.sql

@@ -896,8 +896,8 @@ CREATE TABLE `mail_user` (
   `login` varchar(255) NOT NULL,
   `password` varchar(255) NOT NULL,
   `name` varchar(255) NOT NULL default '',
-  `uid` int(11) unsigned NOT NULL default '5000',
-  `gid` int(11) unsigned NOT NULL default '5000',
+  `uid` int(11) NOT NULL default '5000',
+  `gid` int(11) NOT NULL default '5000',
   `maildir` varchar(255) NOT NULL default '',
   `quota` bigint(20) NOT NULL default '-1',
   `cc` varchar(255) NOT NULL default '',