Lua script: polar mapping a texture for prepping in spherical projection

If you spherically map a texture you may often see 'pinching' at the
two poles. (If the texture is not seamless you'll also see a seam from
pole to pole in the 'back' side.)

The pinching can be avoided by doing a Polar projection correction.
Paul Burke  had a neat algorithm on his website, I've converted it to
a Lua script, so you can use it with the GIMP (if you have the gluas
plugin installed), and of course also with the free or commercial
versions of Project DOgwaffle, and Artweaver (also a free imaging
program for WIndows with gluas/Lua).

http://www.thebest3d.com/dogwaffle/lua/polar

If you know of other imaging tools which have Lua scripting, or is
there a polar mapping tool in Blender?, please let us know.

Would love to see someone take this into a Python version too :-)