By John Revill ZURICH (Reuters) -The Swiss National Bank ramped up foreign currency purchases during the second quarter, data showed on Tuesday, as the central bank reacted to appreciation pressure on the Swiss franc after President Donald Trump announced tariffs on U.S. imports in April. The central bank's purchase of 5.06 billion Swiss francs ($6.36 billion) worth of foreign currencies in April-June was its highest quarterly level of foreign currency interventions for more than three years. The SNB ...