[1.11.2] Natura overworld trees can't be farmed with Forestry multifarm

[LachimHeigrim]

It seems all Natura's overworld tree generating code (except for sakura) ends up checking for soil under sapling, which is implemented as hard check for dirt or grass.

Forestry multifarms unfortunately plant stuff on their own block humus so while saplings get planted okay, they will never grow.

[temp1011]

https://github.com/ForestryMC/ForestryMC/commit/d43cc63367a1c3193376f91e52028b1ec38a18db these now work, however there are other problems to be solved...