LONDON (Reuters) - A stampede to safety sent benchmark government bond yields tumbling on Monday, hoisted the Swiss franc to its highest in nearly two years and gold to a 10-week peak, while oil veered close to bear market territory.After a torrid May that wiped $3 trillion off global equities, worsening trade tensions and the broader economic backdrop made for a jarring start to June.European shares and Wall Street futures both slipped further after Beijing sent another shot across Washington's..