By VLADIMIR ISACHENKOV MOSCOW (AP) — Crushed into the pilot's seat by heavy G-forces, Soviet cosmonaut Yuri Gagarin saw flames outside his spacecraft and prepared to die. His voice broke the tense silence at ground control: “I’m burning. Goodbye, comrades.” Gagarin didn’t know that the blazing inferno he observed through a porthole was a cloud of plasma engulfing Vostok 1 during its re-entry into the