'Mark ``field`` to be recomputed on ``records``.'

def add_todo(self, field, records):

    recs_list = self.all.todo.setdefault(field, [])
    for (i, recs) in enumerate(recs_list):
        if (recs.env == records.env):
            recs_list[i] |= records
            break
    else:
        recs_list.append(records)
