proposal: change postgresql to use SERIAL

I'd like to propose changing the IdGenerator stuff for PostgreSQL based 
on the assumption that auto-increment/sequence columns are now commonly 
specified using the SERIAL datatype (which essentially behaves like an 
auto-increment column rather than a traditional sequence).  This would 
change the PgSQLIdGenerator class to return AUTO_INCREMENT rather than 
SEQUENCE as the id generator type.

Is everyone OK with this change?  This will necessitate that next Creole 
version be 1.1, as this could break some backwards compatibility (though 
technically Creole is designed such that your application can check 
whether the driver uses sequence/auto-increment and behave accordingly).

Cheers,
Hans