* Dollar drops to 6-1/2 month low as data fails to budge Fed rates view* Gold firm on safe-haven bid, wheat at 13-month high on Ukraine, Russia tension* China yuan firms, talk of central bank intervention helps* Shares driftBy Marc JonesLONDON, May 6 (Reuters) - The dollar fell to a 6 1/2-month low on Tuesday as investors looked past signs the U.S. economy is emerging from a winter-induced slowdow