By DOUG MELLGREN, Associated Press Writer April 19, 2002, 4:42 AM EDT OSLO, Norway -- Thor Heyerdahl, the Norwegian explorer who crossed the Pacific on a balsa log raft to prove his theories of human migration, has died at 87. Heyerdahl, whose book "Kon-Tiki" on the daring 101-day voyage sold millions of copies, stopped taking food, water or medication in early April after being diagnosed with a terminal brain tumor. He died Thursday night in his sleep at home in Colla Michari, Italy, said his son, Thor Heyerdahl Jr. Heyerdahl had been hospitalized near there in late March when he...