matplotlib Code

Fixed previous set_ticklabel modification.

Prevent contour lines from appearing in legend

Add masked_demo.py to backend_driver.py.
This will help us check that changes don't break basic
masked array support in the plot command.

cleanup

fixed up date demos

added autofmt for date plots

fixed bug in lines.py units support that broke masked array plotting

Modified 'set_ticklabels'. This did not appear to actually set the tick labels.
This could be demonstrated with a 'set_ticklabels' immediatly followed by a 'get_ticklabels'
and they would not match.

Added a line to Axis.convert_units that gets the proper converter if None is set.
Removed a line from Axis.set_units that sets the converter to None if the units is set to None.