In dirtree_datafiles __init__, get the path and filter through explicit arguments.
Getting it out of the options argument is still supported, but deprecated.  There's no need to
carry paths and filters around, other than to initialize this object.
Clean up the beginning of the script - where paths and options are identified, etc.
Now there are two ways to run diagnostics from a Python script - specify your files inside
two Options objects, or create two filetabls and supply those instead.  Command-line usage
is unchanged for the moment.