matplotlib Code

more minor reformatting

Remove unnecessary data copying from draw_quad_mesh

more docstring tweaks

Add experimental "pcolorfast" for fast interactive pcolor plots

This will need more discussion and work, but it illustrates
the potential for very fast pcolor-type plotting with all
three grid types: uniform, irregular but rectilinear, and
general quadrilateral.

Use new update_dict from ScalarMappable in QuadMesh

Remove trailing whitespace.

Let to_rgba return uint8; track changes to cmap

Images require rgba as 4 uint8s, so it is more efficient
to generate these directly in to_rgba than to generate 4
doubles and convert them later.

The tracking of changes in ScalarMappable was handling
communication between objects, but was not keeping track of
when to_rgba needs to be rerun. A dictionary was added
to do this.

further streamlining of docstrings

add 'f' to coastline resolutions. Reformat unsupported projection message.

port over the rest of Eric's changes from trunk