Alpha transparency in texture maps

Right, so, I did a quick dib at this and implemented alpha mapping I guess.
See the screenshot (I guess the blackish lines around the transparent edges
are "z-fighting"?)

The only thing that still is missing somewhat is:
When using alpha maps, opacity should be 1.
However, the current approach (with opacity) does not permit this, so all occurrences (in shading/renderModule.js)
of renderOpaqueNodes need to be replaced with renderTransparentNodes I guess.

The best solution here would be calling renderTransparentNodes instead of renderOpaqueNodes when
node.texState.hash != "__scenejs_no_tex" as we currently only create new textures as RGBA anyway.

Or we could also argue that all non-transparent nodes have an opacity and alpha of 1 anyway so that therefore the renderOpaqueNodes isn't needed at all and we can use renderTransparentNodes everywhere which seems like the best solution to me tbh (I don't know whether that'd have some performance impact though).

In the Sirikata fork of GLGE - a "discard" keyword in GLSL, used for alpha transparency by the looks of it:

http://github.com/sirikata/GLGE/commit/67c1ae074419927eb629bdad1f44...

Perhaps not quite applicable to this case, but worth mentioning!

"The discard keyword can only be used in fragment shaders. It causes the termination of the shader for the current fragment without writing to the frame buffer, or depth."

I guess this might indeed be a nice feature in case the user wants to set a lower limit to transparency(possible performance boost?). I think that that should be an option for the scene or so though.