Updated the data system to take the LOD center for loading chunks as an
argument instead of trying to look up the PLAYER position. This was
necessary to get the test_worldgen.h unit test working, as it doesn't
spawn the player.

-Peter Mawhorter
Messed with the branch generation algorithms a bit, which were kinda
broken. They're better now, but still not working as well as they used
to be.

-Peter Mawhorter