fix for chatroom_msg table definition

The SQL statement in chatroom.install calls for the chatroom_msg.msg field to be longtext. This is not good. It wastes space and makes MySQL perform worse. Since chat messages are hardly ever in the vicinity of 4,294,967,296 bytes long, wouldn't it make more sense to speed the db up by defining that column as varchar(255), or, if you really need more, TEXT(512)?

      $ok = $ok && db_query("CREATE TABLE {chatroom_msg} (
        cmid int(11) NOT NULL AUTO_INCREMENT,
        ccid int(11) NOT NULL,
        uid int(11) NOT NULL,
        msg_type varchar(64) NOT NULL,
/*        msg longtext NOT NULL,*/
		msg text(512) NOT NULL,
        session_id varchar(255) NOT NULL,
        recipient varchar(255) NOT NULL,
        modified int(11) NOT NULL default '0',
        PRIMARY KEY  (cmid),
        KEY ccid (ccid),
        KEY session_id (session_id),
        KEY recipient (recipient),
        KEY modified (modified)
      ) $utf_declaration;");
      $ok = $ok && db_query("CREATE TABLE {chatroom_msg_archive} (