track settings that share the prefix are kept
  hgPcrResult_imgOrd         3                                        kept
  hgPcrResult_targetStyle    box                                      kept
a result pair of trash files is kept
  hgPcrResult_hg38           two trash files                          kept
  hgPcrResult_hg38           two trash files and a target             kept
a result that does not name two trash files is dropped
  hgPcrResult_hg38           3                                        dropped
  hgPcrResult_hg38           a psl file outside the trash             dropped
  hgPcrResult_hg38           a primer file outside the trash          dropped
the exclusions are exact names, not suffixes
  hgPcrResult_hg38_imgOrd    two files outside the trash              dropped
  hgPcrResult_imgOrdx        two files outside the trash              dropped
