order_id field in {uc_payment_cim} should be int not mediumint; storing cim_ppid breaks otherwise

Figured it out. The order_id column is set to a mediumint, which does not have a high enough max value to compensate for order_id which is usually an int(11). Changing the title to reflect this, will write a patch shortly.

Better title, and here's a patch. Before this value, every order_id stored in the table would have a value of 8388607.

My patch also updates the table to have order_id be a primary key; this is needed so that we can use db_write_record() to insert new rows and to update them as needed. You should never have more than one ppid per order, as that could lead to returning the wrong value (especially in cases like this).