code: def check_for_uncombined_files(self):
          
          wd_files = os.listdir(self.WD)
          if self.data_model_num == 2:
              ftypes = ['er_specimens.txt', 'er_samples.txt', 'er_sites.txt', 'er_locations.txt', 'pmag_specimens.txt', 'pmag_samples.txt', 'pmag_sites.txt', 'rmag_specimens.txt', 'rmag_results.txt', 'rmag_anisotropy.txt']
          else:
              ftypes = ['specimens.txt', 'samples.txt', 'sites.txt', 'locations.txt']
          uncombined = set()
          for ftype in ftypes:
              if ftype not in wd_files:
                  for f in wd_files:
                      if f.endswith('_' + ftype):
                          uncombined.add(ftype)
          if uncombined:
              msg = 'It looks like you may have uncombined files of type(s) {} in your working directory.\nYou may want to go back to Step 1 and finish combining all files.\nIf you continue, the program will try to extract as much information as possible from your measurement file.'.format(", ".join(list(uncombined)))
              dlg = pw.ChooseOne(self, 'Continue anyway', 'Go back', msg, title="Warning!")
              res = dlg.ShowModal()
              if res == wx.ID_NO:
                  return
          return True
docs: Go through working directory and check for uncombined files.
          (I.e., location1_specimens.txt and location2_specimens.txt but no specimens.txt.)
          Show a warning if uncombined files are found.
          Return True if no uncombined files are found OR user elects
          to continue anyway.