By Yoruk Bahceli LONDON (Reuters) -Reserve managers tend to buy the dollar when it weakens and sell when it rises, suggesting they might play a lesser role in driving the greenback than private investors, Standard Chartered said in a note on Thursday. Demand from central banks managing trillions of dollars worth of currency reserves is seen as crucial to the dollar's position as the world's top safe-haven currency. But U.S. President Donald Trump's confrontations with longstanding allies over trade and ...