New generic function LandSize returns the total size of ranges in a land (if the land supports it). Implement it for all Land classes.
The MVFF pool class doesn't have to maintain its free size any more: it can just call LandSize.
Move re-entrancy protection from CBS to Land. This allows us to remove some CBS functions. (But requires some adjustment in failoverDelete.)
In MVFF, do more checking of mvff->total.