use _makeChunk to create unloaded chunk objects
use _makeChunk to create unloaded chunk objects

relight-all failed because it was scanning _loadedChunks when it should have been testing for the chunks' existence

also, generator comprehensions

ahh2131/mchisel,ahh2131/mchisel,codewarrior0/pymclevel,arruda/pymclevel,codewarrior0/pymclevel,mcedit/pymclevel,mcedit/pymclevel,arruda/pymclevel