Suppress compiler warning
Fix visual_scale for NDT_PLANTLIKE being set too small
Temporarily set default biome in builtin

This should probably be removed when minetest_game has proper biomes.
If I hear "the whole map is just stone!" again after this, I am going to detonate.
Fix visual_scale for plantlike nodes (again)

fixes #1989

move the plant to the bottom of its node properly, without affecting its scale.  See isue #1989
Re-add hacky fix for underwater grass, to fix mgv7 user's biomes