MOSCOW (Reuters) - The mystery surrounding missing Russian presidential candidate Ivan Rybkin deepened Monday in a swirl of media speculation about his fate, Kremlin silence and attempts by officials to play down the affair. The bizarre disappearance of Rybkin, 57, a fierce critic of President Vladimir Putin, on the night of Feb. 5 injected drama into the run-up to a March 14 election that Putin is widely expected to win easily, securing a second term.Rybkin's wife, Albina, suggested that the ally of exiled entrepreneur and Putin foe Boris Berezovsky had been kidnapped. But even his aides were wary of that...