TOKYO -- The rapidly falling dollar marked a milestone in Japan as it fell below ¥100 for the first time in 12 years, threatening Japan's exporters and increasing the likelihood that the world's No. 2 economy would slow down significantly.The dollar dropped to as low as ¥99.80 during Asian trading Thursday. It crossed the psychologically important threshold of ¥100 for the first time since November 1995, when it also reached ¥99.80. The dollar also sank to all-time lows of $1.5625 per euro and flirted with parity against the Swiss franc, sinking to 1.0045 francs. Against the British pound, the ..