MPC dryrun traceability

Provisional naming during dry runs now uses a counter on the measure3 directory (in the same sort of way non-dry-runs do) so that restarting the application does not start the counter from 0.  Names are of the form DRY0001.  The counters are per epoch/field like with non-dry-run so the counter may restart for different input files.  However, when in dry run mode MPC files also have their reals.astrom filename prepended, so there should be no chance for conflicts.  Prepending the input filename also increases traceability when testing things out.  #175