I've added code that does precession of the axes, as well as a start of a general rewrite of the celestial sphere code. The patches are at
http://www.gnacademy.org/twiki/bin/view ... Extensions
I've also reorganized the code so that there are five or six individual patches rather than one huge patch, so that you can pick and choose what you want to add to the code.
The general rewrite of the celestial sphere grid code allows you to in principle create a grid with any pole. This means that it should be easy to use the code to draw alt-azi, ecliptical or galactic coordinates.