Change _move_lockdir to update the props in memory, not just on disk.

We were correctly updating the props on disk, but then we would try to
access props again after calling _move_lockdir(), and the in-memory
props would still have the old lockdir location.  Now we update the
in-memory data structure at the same tim we update the on-disk data
structure.

This should cause finish_with_relock() to work again -- in particular,
the POSSIBLE_NEXT_STEPS update it does after relocking.

Auditors: chris

Test Plan:
Fingers crossed.