Fix number item issue with buyer NPCs

The intermediary numberitem stack wasn't being deleted if the NPC
already had a stack of that item, and for rainbow ferns this was causing
dangling timer issues. These are now deleted properly.
Hstone, Kocatan room formatting

Also made Heartstones non-disposable; fixed spelling errors in resources
and some debug code in Kocatan Sewers.
Up Chuk Creek graphical error fixes

Some sidedefs didn't have textures, so were showing the skybox. Raised
the ceiling in the tunnel near exit to 'first' sewer screen to prevent
players seeing skybox through the low roof.