matplotlib Code

added latmax kwarg to drawparallels and drawmeridians (patch from Chris Murphy).

Added Karen Tracey's threading_test.py.

print message if LightSource not found

Make images handle invalid values as if masked.
A little cleanup and docstring addition to image.py was included.

lightsource --> LightSource

moved agg caches to instance namespace for thread safety

changed name of lightsource class to LightSource to conform to coding guidelines.

applied Gael's sphinx patch

Contouring handles nans in Z via masking.
(The bug in filled contouring with internal masked regions
remains.)

ticker typo fixes