[fixed] Material is invisible if environment is enabled

[dgud]

I render transparent faces in several passes, to get decent result without sorting (in view dir) every transparent face I partition transparent faces in two groups, almost transparent and almost opaque.
So I chose a value that I thought was ok: > 0.85 is opaque.

Simplified wings render:
almost transparent objects
almost opaque objects
opaque objects

Since wings is a modeler and not a render tool, we need to find a decent and fast approximation,
and rendering transparent objects without raytracing (or sorting) is hard.

The current solution is the best I have come up with so far, there will always be corner cases that
just don't work. If someone can come up something better it would be great.