fix filters and mese filters not working correctly
chests, furnaces are not supposed to connect to tubes from the front sides
Fix glitch in tube autorouter
(brain-o in how I was handling unknown/bad nodes being passed to it.  this
works better and lets the code do its job properly).
ok, on second thought, allow tubes to connect to the fronts.  Also, define
top-side overlays for furnaces.
fix copy&paste error