clean up id creation a little
clean up id creation a little
Improve plot titles, and provide plots with a new 'source' attribute which is used in the subtitle.
Improve the short name created by dirtree_datafiles.short_name().  If a file filter is applied,
the filter is identified.  To support this, some of the filters have a new mystr() method which
identifies the filter as briefly as possible
New method basic_filetable.source().  It identifies the source of the filetable's data,
for use in plot titles, filenames, etc.
better filename for writing plot data