code: def add_patch(self, pset, augref):
          
          try:
              path = [ self.add_prefix(c, augref)
                       for c in augref.arg.split("/") if c ]
          except KeyError:
              # augment of a module that's not among input modules
              return
          car = path[0]
          patch = Patch(path[1:], augref)
          if car in pset:
              sel = [ x for x in pset[car] if patch.path == x.path ]
              if sel:
                  sel[0].combine(patch)
              else:
                  pset[car].append(patch)
          else:
              pset[car] = [patch]
docs: Add patch corresponding to `augref` to `pset`.
  
          `augref` must be either 'augment' or 'refine' statement.