Fix a few issues related to recent database changelog updates

Hi,

I had a few issues with the new DB changelogs submitted in change 24ee418f3f307bbc0e40dafbbdd682c01c8f482d:
* HSQLDB did not like setting a column to non-NULL with no default value given. I gave a default value to make it happy, but maybe there is a better way to fix this? Let me know if you would like me to alter this change...
* PostgreSQL rejected a few SQL update statements too.

These changes seems to work fine with HSQLDB and pgSQL, but I did not try with mySQL or MS SQL.

CommaFeed is great! Thanks!