Rock/Dirt generation code, ant slowdown through harder dirt, and a few fixes too

Pretty horrible code for making the rocks/dirt patterns. It's also pretty slow, it tends to take a few seconds to generate the level now with the current settings. Feel free to discard this part of the pull request if you can do a better job.

There's also code to slow down the ants in harder dirt, and then a couple of fixes in the TileInfo stuff.