celeron55/minetest — pull request #378 by RealBadAngel (2012-12-30 14:15:01+00:00)
Title: Cave gen fixes.

Forbid creations of caves above ground level (this will fix floating dirt bug and also should speed up generation since LOTSA caves were generated in the air).
Allow placin blobs of mud and gravel only below water level.
Changes wont let cave gen to destroy generated contens like trees for example.