Given the name of the PC, return the database identifier.

def _id_for_pc(self, name):
        """ Given the name of the PC, return the database identifier. """
        if not name in self.pc2id_lut:
            self.c.execute("INSERT INTO pcs (name) VALUES ( ? )", (name,))
            self.pc2id_lut[name] = self.c.lastrowid
            self.id2pc_lut[self.c.lastrowid] = name
        return self.pc2id_lut[name]