matplotlib Code

Render all the fonts in each mathtext expression to a single image buffer
(memory and time savings).
Add support for getting raw image data for mathtext expressions.
Add mathtext_wx.py example showing how to put mathtext expressions
into controls.

Fix docstring

Make horizontal line drawing more consistent across all backends.
Fix but in ft2font glyph rendering for glyphs with a left offset.

Remove "deprecated conversion from string constant to char*" warnings.

Improve horizontal lines in mathtext in Agg backend.

Fix bug with SVG non-math text

Fix bug with PDF non-math text

Improve font rendering considerably using a vertical hinting hack.
Hinting is disabled for all of the "vector" backends, to correct
spacing problems.

Reverting last change since it breaks on gcc-4.2

Attempting to reduce compiler warnings for gcc-4.2 (which I don't
have, but Darren Dale has reported some new warnings).