FRANKFURT (Reuters) - European Central Bank chief Mario Draghi took a swipe at Washington on Thursday for talking down the dollar, a move he said threatened a decades-old pact not to target the currency and might force his bank to change its own policy. Singling out the euro’s surge as a source of uncertainty, Draghi said any unjustified move could force the ECB to rethink its strategy as a strong currency could put a lid on inflation, thwarting its efforts to lift prices.