Add bounds updating to plDrawableSpans::composeGeometry

This is important because BuildSpaceTree uses the icicle bounds. I have no
desire to calculate plGeometrySpan bounds in Python, so I need a way to
generate them before the call to BuildSpaceTree node. Note that calcBounds
operates on the encoded vertex buffer.
Return index of added DIIndices and SourceSpans

This makes creating the plDrawInterface and plDISpanIndices a little bit
easier from Python. And there's less need for all of tha crazy looping in
buildDIIndices...
Initialize plGeometrySpan

We don't want random grabage from the heap being used in
plDrawableSpans::composeGeometry... Or I don't.
Actually set the materialIdx...
Fix pyTempVertex position/normal setters
Merge pull request #43 from Hoikas/korman-draw

DrawableSpans Sanity++