We now harvest information about texture images throughout the export
process and don't pull the trigger until we're totally done. There are
still some issues with regard to confusing UI, but we'll get to it.
If we don't reference the SceneNode from each SceneObject, we can't get
the SceneNode from an ObjInterface. For some strange reason, plClient
overrides the plDrawableSpans SceneNode at runtime. This caused the DSpan
to be removed from all nodes.... :/
It appears that we were storing PyHSPlasma objects in class attributes, so
they were being held after the plResManager went away--therefore their
keys were nuked. We should probably be holding keys and not objects, but
this fix works regardless.