BEAR ANY BURDEN Apparently Sen. John Kerry cares enough about what Sen. Ted Kennedy thinks of him that the presumptive presidential candidate called Kennedy to inform him that he would not cross the Boston Police Patrolmen's Association picket line at the U.S. Conference of Mayors in Boston on Monday. Kerry was scheduled to speak at the conference, but abruptly pulled out. While a Kennedy Senate staffer said that the senior senator appreciated the courtesy call, the two men remain cool. "Kerry should have been speaking to us about the problems in Boston weeks ago," says the Kennedy staffer. "One good...