handle DB errors gracefully

[ehabkost]

[10:29:41] [Notificar] passerd-bot para #twitter- error refreshing feed: (OperationalError) disk I/O error u'UPDATE user_vars SET value=? WHERE user_vars.id = ?' [u'10220359684', 3]
[10:36:26] [Notificar] passerd-bot para #twitter- error refreshing feed: The transaction is inactive due to a rollback in a subtransaction. Issue rollback() to cancel the transaction.
[10:40:37]  !
[10:40:38]  error refreshing: The transaction is inactive due to a rollback in a subtransaction.  Issue rollback() to cancel the transaction.

And now the server is dead:

[10:40:45] [Informações] Conectado, autenticando...
[10:40:48] [Notificar] -passerd.server- *** An internal error has occurred. Sorry. -- : The transaction is inactive due to a rollback in a subtransaction. Issue rollback() to cancel the transaction.