Get rid of the civicrm_group_contact_cache table

I always wondered why we have the group_contact_cache table ... we could very well cache the smart group results in the group_contact table (with status = 'Smart') ... this way any queries on groups would just look at one table rather than have these Russian doll joins and ors!

To list all contacts in a smart group:
SELECT contact_id FROM civicrm_group_contact WHERE group_id = xxx AND status IN ('Added', 'Smart');

Then, to refresh the smart group:
DELETE FROM civicrm_group_contact WHERE group_id = xxx AND status = 'Smart'; INSERT IGNORE INTO civicrm_group_contact ... (results from smart group query)

The INSERT IGNORE with a primary key on (group_id, contact_id) would take care of not adding smart group query results that already have an 'Added' or 'Removed' status.