use twitter_id as id in users table

[kykim]

is it possible to change the migration to look like this:
create_table :users. :id => false do |t|
t.integer :id, :limit => 8 # force column to bigint in mysql
...
end
add_index :users, :id, :unique => true

if this is possible, then we can have the id in the users table match the id we get from twitter.
we'd have to change the GenericUser model a bit to handle this, but i think it should work.