Adding NEW_BITMAP flag to the bitmap_mode enum
Make use of NEW_BITMAP to avoid wasted read. Simplify the bitmap_from_filename interface
Change to new bitmap_from_filename interface
Modify tests to match bitmap_from_filename changes

Change to match the new interface. Remove the two resize tests
since that behavior (resize without create) is no longer supported.
Do not terminate when we fail to create a filter...
Remove new files if we fail to initialize the bitmap
Actually use the extra_flags
New interface to register filt manager clients

Adding a new interface that uses `filtmgr_client_checkpoint`
and `filtmgr_client_leave`. Checkpoint is used to register and
periodically update the latest seen version, while leave is used
when a thread no long needs to make use of the filter manager.

This change allows the vacuum thread to more safely determine
the last version of all clients. Previously, the client list was
limited to the workers using a fixed size array. This approach
did not allow the flush and cold unmap threads to be accounted for,
and thus had potential safely problems. The new interface is more
accomadating and can even allow for things like temporary threads
that need access to the filter manager.
Background threads register with the filter manager now
Update from worker_checkpoint to client_checkpoint
Worker threads first do a client_checkpoint before entering the network stack
Better handling of an in-progress delete

We now do a much better job of detecting that a delete is in
progress and avoiding doing a conflicting create at the same time.
Previously, due to the MVCC architecture it was possible to have
a filter be deleted in version V, and then created in V+1, even
though the vacuum thread has not yet cleared version V.

This would cause a duplication of the internal buffers, and eventually
the vacuum thread will do a delete of version V, and the on-disk
contents would be lost.
Adding an integration test for in progress drop
Adding method to force a vacuum for the tests
Adding a few force vacuums for the tests
Updating the changelog for 0.6.0
Tag the git sha