Fatal error when using the textfile login handler + MySQL master/slave. No error when master/slave is disabled.

This is the error:
Fatal error: Call to a member function setAttribute() on a non-object in
kernel/classes/datatypes/ezuser/eztextfileuser.php on line 282

The patch fixes this by ensuring the master database is used for the whole request.

Steps to reproduce

• Enable Mysql master/slave
• Enable textfile login (csv)
• Login a textfile user

This will crash in some cases, depending on whether the slave server will be used.