Extensions will frequently want to add new fields to the database tables. Doing this cross-DBMS today is kind of clunky. A new method in the database class should solve this. Maybe something like:
function add_field($table_name, $field_name, $field_type, $allow_null, $default_value, $after_field = null)
The method could then translate certain field types into ones that are supported. For example, if the method would get called with $field_type set to TINYINT(1), it would get translated into SMALLINT for PostgreSQL. The $after_field parameter should be ignored for all but MySQL.
On top of this, a simple drop_field($table_name, $field_name) should be implemented.
