Fix for libpng-1.4 compatibility
Added gnu0 platform to setupext.py (Benjamin Drung)
add Colorbar.set_ticks and Colorbar.set_ticklabels
Let setup.cfg customize the base directory for libs and includes
a minor fix of blocking_input.py
Modified EllipseCollection for closer compatibility with Ellipse patch.
Make plot_directive use a custom PlotWarning category.
minor refactoring of the ps backend
make backends registerable
fix axis_artist bug
