unload chunks during a chunk-aligned copy, also saving them.
unload chunks during a chunk-aligned copy, also saving them.

edges will have wrong lighting if a crash happens, but whatever

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