PSX mission tweaks

Better name string, and null out exit rules so that DOOM II MAP31/32 ->
16 do not apply (rest of logic is handled through EMAPINFO)
Remove ylookup and columnofs from renderer

Thanks again to dr_sean for figuring out these are a big source of cache
misses at high resolutions.
Merge commit '584c6997ae74996292bda07220fe6df0dc33dbc0' into AutoDoom