Compile NCPCompatBukkit against 1.4.7-R1.0, since more is not needed.
Remove hopefully not needed extension for y-bounds for isOnGround.
Add comment.
More caching for on-ground checking in PlayerLocation.

Remember the minimal yOnGround for having found ground and the maximal
yOnGround for not having found ground. Does not apply for all
xz/y-margin parameters, yet.