Forestry Tree modhelper as submodule

This PR sets up the Forestry/ExtraTrees farming compatibility as a submodule in git. I think this will work better than PRing each individual change. 

Any time the submodule needs updated there is an included script to do that. (I'll probably run it myself after any significant changes and PR the resulting commit, still far cleaner than PRing each change imo).

As long as you check the box in jenkins it will compile MFR with the submodule included. 
 
![make_sure_this_is_checked_on_jenkins](https://f.cloud.github.com/assets/1806869/758486/0fdde656-e737-11e2-9b8e-006481067852.png)

You won't see the code locally unless you clone with the --recursive flag. The buildscript has been tweaked to run fine with or without the module being cloned.