Improved identification of plotsets - extract the set number from the name, before comparing the
user's plot set requests with the list of available ones.
Minor name change, v to vcanvas.
minor testing change
a small simplification by using path2filetable(); and change the test data
Set the path option to a dictionary in opts1.
Better default treatment of seaons
__repr__ should return a string, not a tuple
Index all variables in the filetable.  It doesn't work to try to limit it to the variables
the user thinks matters.
Add all the keyword arguments available in dirtree_datafiles.__init__()