This is in line with simpler and still existing behaviour where a default parcel is created if no parcels are in storage at all.
Making this change as another step to address current problems with spurious parcels occasionally being created.
Also adds regression tests for different load behaviours depending on existing stored parcel data.
Relates to http://opensimulator.org/mantis/view.php?id=7035
This is to prevent an immediate problem in http://opensimulator.org/mantis/view.php?id=7035 where a development code bug occasionally overlays all the existing parcels with a blank parcel owned by the estate manager and to gather more data.
My guess is that this parcel is being created by the new code in LandManagementModule.GetLandObject(), probably some race between threads since this only happens occasionally.
Adds regression tests for this case and for parcel subdivide.