Add an argument to _results() methods, nothing done with it here; used for changing output grid in uvcdat.py.
Also a minor spelling correction, and some harmless work-in-progress.
When a variable is regridded to do model-obs difference, save the regridded data.  It's done with a global variable.
Later I'll want a better way of doing it (you can't simply put it in the mv because that makes for output problems),
but this will work for the moment.
When computing results of a plot_spec object, there is a new optional argument newgrid.
With the default, newgrid=0, everything is the same as before.
With newgrid!=0, if a z variable has been regridded for a model-obs difference or similar
purposes, the regridded version will be substituted for the original z variable.
This is somewhat experimental code.  In the future newgrid<0 will mean the coarsest grid
in use and newgrid>0 will mean the finest grid in use; "in use" means for the current
composite plot.
I also corrected a typo or two.