matplotlib Code

axes_grid: fix broken spine support

Add set_color() convenience method to Spine class

Spine is now derived from Patch

improve the animation_blit_qt4 example

added spine autodocs

mplot3d: add examples, fix NaN bug

make default argument to Axes.get_xaxis_transform() not raise error

I made this a separate commit from the previous one because it may be
useful to see the errors that arise if get_xaxis_transform() or
get_yaxis_transform() are called with no arguments. This would allow
one to figure out which code paths are calling these methods and fix
them if needed rather than silently partially succeeding.

Arbitrary spine placement

mplot3d: contourf3d, bar / zordering

Fix broken example.