Fix rock passability in snow, winter, temperat

There were some mistakes in passability for some cliffs and a rock. I fixed them in these tilesets.

There are a few "edge cases" where it's ambiguous whether a given tile should be built upon which I didn't touch. If someone is neurotic, they can ask me for screen shots and I'll show them.

Will work on desert next. There are many more mistakes there so it will take longer.