In BlockPlacementStrategy.getNBestMoves() (the meat and potatoes of that class)
starting lesserIndex from 0xffffffff instead of the old 0x7fffffff. We can
use the high bit because within the long key the bits find themselves in the
lower 32, so they don't interfere with proper ordering of the long keys.
I checked the code and the keys themselves are not use anywhere; only their
order is important.
