* Add an option to limit the recursion level depth in BSP tree

* Add an simple option to subdivide long, stretched triangles so that
  SIMPLE_SORT can still be used for simple, non-intersecting geometries
  (cf. Olivier Couet's long cylinders at Cern) where BSP_SORT is very
  slow due to the presence of many, many curved surfaces

* do we really need gl2psEnable(GL2PS_BLEND)? Couldn't we just check
  what's in rgba[3] and try to do the "right thing" right away?
  Update Thu Jul 20 14:51:33 2006: that's what I do now for SVG and it
  works pretty well. We could probably significantly simplify the PDF
  code that way.

* Think about a way to provide a progress indicator through a
  callback. Not easy for BSP trees due to the recursive
  implementation.
