[PythonCAD] Entity drawing using Cairo

[Art Haas]

Hi.

I've sent some new code up to the repo which will utilize Cairo routines
for drawing some of the entities in PythonCAD. The GTK+-2.8 release
uses Cairo, and the most recent PyGTK releases have bindings to the
needed calls, so if you are running a recent PyGTK/GTK+ package combo
then the Cairo routines will be used. So far I've added routines for
Segments, Circles, Leaders, Polylines, the different construction
entities, and TextBlocks. I'll be adding the code for Arcs and the
dimension entities soon. The code is still being tinkered with somewhat,
so things may look a little odd every now and then. If you are running
PyGTK/GTK+ releases without Cairo abilities then the existing drawing
routines are used.

Using Cairo routines for drawing will be required for adding support for
the GTK+ printing abilities added in GTK+-2.10. I hope to add support
for this new GTK+ feature shortly, but it will not be in the next
release.

The new code is just an 'svn update' away for people using Subversion.
Feedback welcomed if you see problems or have suggestions.

Art
-- 
Man once surrendering his reason, has no remaining guard against absurdities
the most monstrous, and like a ship without rudder, is the sport of every wind.

-Thomas Jefferson to James Smith, 1822