matplotlib Code

Fix memory reservation for curve to line segment conversion.

[ 1901410 ] Newbie bug report: clip_on set to False actually True

Formatting and minor efficiency improvement.

Remove case-sensitivity for backend selection. (Not a user-visible problem)

Fix memory leak in Gtk backend.

Fix memory leaks and uninitialized memory errors discovered with valgrind.

Add valgrind memcheck support to backend_driver.py

Don't cache many-sided unit regular polygons -- just the small ones --
otherwise we could end up caching many large things.

Remove debugging code.

Fixing picking on masked arrays (Thanks Andrew Straw)