Duplicated rows in nat table

There is not a proper primary key on the table, so duplicates can (and, at least in my case, *are*) being created.

Since node.vid is now included in this table, the primary key should probably be something like:

PRIMARY KEY (nid, vid)

This came to my attention only because I'm writing a module that pulls from the nat table and causes problems unless I include a 'group by' clause on the nat table, which really shouldn't be necessary.

The fix would require some code to de-dupe this table and then put a proper primary key on it.

Duplicate rows are a good source for hard to find bugs.