matplotlib Code

Can't drag zoom on a polar plot.
Finessing Agg drawing quality a little bit.

Increased coverage of backend_driver.py to include almost everything
in axes.py. Lots of little bug fixes.

Initial pass of Gtk, Qt, Qt4, Fltk and Wx GUI backends. Lots more
examples passing.

Forgot to svn add these files in last commit.

Separated path utilities from backend_agg

Fix bug affecting legend_auto.py

Reduce tendency to use aliased drawing.

Fix bug that broke draw_image

First pass at working PDF backend.

figlegends work now. (Phew!) Rendering quality fixes drawing
axis-aligned line segments in Agg.