Removed DEFAULT value from SQL query for TEXT field, because on MySQL 5.0 and above BLOB/TEXT types cannot have a default value, which may throw an error on some systems.
See http://dev.mysql.com/doc/refman/5.0/en/blob.html
Added an aditional check for a correct formated date when saving a user. An empty date string may throw an error on some MySQL installations when creating a new user.
Simplified check if date vaule for lastseen is correct
Reduced the SQL statement to creat TEXT columns further to work with SQLite and MySQL
Merge pull request #258 from frab3/master

Fixed two problems which may occur when using MySQL