matplotlib Code

Some examples to go with the last commit.

Lots of sizing and layout tweaks. Support $\sqrt[3]{foo}. The line
meets up with the check mark rather clumsily on the Agg backends due
to rounding errors and lack of subpixel placement... will look into that.

Fix bug in pdf backend (numpy.inf not numpy.infinity)

Update information about mathtext improvements.

Merging mathtext changes into trunk.

Committing in preparation for merge

Important bugfix (many expressions were silently failing)

Support auto-sized delimiters (e.g. \left(\frac{3}{2}\right)).
Commit mathtext_examples.py

rewrote mathext demo to use pythonic api

Fix for get_xheight/get_underline_thickness. Update examples to use
new math syntax.