Fixed two problems which may occur when using MySQL

Hi Bob,
on my test system (Bolt + MySQL 5.6.10) I found two bugs.

1. Creating the database on first run fails, because on MySQL 5 and above TEXT fields cannot have a default value.
![Screen Shot 2013-03-21 at 12 23 17](https://f.cloud.github.com/assets/3841284/285752/05ba4f20-9228-11e2-8cb8-6c99ffcd1b59.PNG)

2. After removing the DEFAULT value from the SQL statement, creating a new user fails, because the lastseen field has an empty value which is not a correct date value.
![Screen Shot 2013-03-21 at 12 25 21](https://f.cloud.github.com/assets/3841284/285754/16c8eb96-9228-11e2-8f11-fd00bb741789.PNG)

I hope my contribution makes Bolt a bit more failsafe with strict MySQL servers. :)