Crash on level generation

[MicroChasm]

Sometimes the game crashes when I generate a level, with this message: there are too many types of entities on a single tile!

[nsmryan]

I've made some progress on this, but it is not yet resolved. There is now a test map which will keep generating levels until the game crashes. I fixed a few small issues for other things, but there is something about vault placement which can still result in the bug in this issue. Sometimes this happens quickly, in the first 10 generated levels, and sometimes not until over 100 generated levels.

At least I do know that it is related to vaults- if you check the map just before and just after vault placement with the "check_map" function, it finds this problem just after vaults are placed.