r-dejagnu-testcase-classify: robustify for large jobs

r-dejagnu-testcase-classify: robustify for large jobs

- reject loading or saving models where NaN's pop up in the weights;
  it's unknown what sometimes causes this, but at least the disk model
  files should be immune

- add a batching option so that all the testruns processed in
  any given epoch may be batched to some at a time for loading & training;
  this is necessary to manage gpu/cpu ram usage

- tweak exception catching to respond rapidly to single ^Cs, whenever