(Adds comment, table, details on dollar and euro contracts) April 1 (Reuters) - Speculators slashed bullish bets on the U.S. dollar for a fourth straight week, with net longs falling to their lowest in nearly two years, according to Reuters calculations and data from the Commodity Futures Trading Commission released on Friday. The value of the dollar's net long position fell to $4.65 billion in the week ended March 29, from $5.91 billion the previous week. dollar net longs came in be