PROTESTERS FORCED cancellation of classes at the University of the District of Columbia for the third day Friday as part of a drive to remove most of the school's trustees, whom they consider insensitive to student concerns . . . SUSPECTED PRO-IRAQI terrorists threw three grenades into two crowded cafe terraces in Paris near a French military base in the East African nation of Djibouti, killing the 9-year-old son of a French officer and wounding at least 16 other people, officials said.