Draw closer faces of tiles after farther faces of tiles.
Draw closer faces of tiles after farther faces of tiles.

The CPU time cost in 'drawing' phase of adding this code
for pressure_tunnel appears to be 0-3% (the range is due
to not having more measurement precision).

Acceptable, considering that it lets us make the faces
different colors.

Well... it also makes it *harder* to make, e.g.,
the top face a different color, because it's harder
to find out which face is the 'top' one now! But it
should be quite doable.

If we come up with a different way to arrange for
drawing tile-sides in the right order when it matters,
then I'd be happy to scrap this approach, though I don't see
a superior way for right now (for tiles that are translucent
and have different faces different colors).

Lasercake/Lasercake,idupree/Lasercake,idupree/Lasercake,Lasercake/Lasercake,elidupree/Lasercake,elidupree/Lasercake,idupree/Lasercake,idupree/Lasercake,Lasercake/Lasercake,elidupree/Lasercake,idupree/Lasercake,idupree/Lasercake,elidupree/Lasercake,Lasercake/Lasercake,idupree/Lasercake,elidupree/Lasercake,elidupree/Lasercake,elidupree/Lasercake,Lasercake/Lasercake