Fix typo in k5test.py

The principal/principle confusion strikes again.
Unlocked db2 KDB iteration

Try to make an optional db2 iterator that unlocks (and therefore
closes) the KDB between iterations, to allow large KDBs to be dumped
without blocking writes for a long time.

This is a hackish proof of concept.  It won't work for all consumers
of db_iterate, especially ones that need to hold other locks while
iterating.