set Agg backend in plotclaw.py for some systems where it complains about DISPLAY not being set.
Merge pull request #103 from rjleveque/plotclaw_Agg

set Agg backend in plotclaw.py
Got masking to plot correctly by modifying geoplot.surface
Merge branch 'master' into googleearth
Got rid of debug trace
More masking fixes - it should now work