By KHALID TANVEER and RIAZ KHAN 2010-08-03T12:02:25Z KOT ADDU, Pakistan (AP) -- Floodwaters that devastated Pakistan's mountainous northwest surged into the heartland Tuesday, submerging dozens of villages along bloated rivers whose torrents have killed at least 1,500 people and put 100,000 at risk of disease. Fresh rains in the hardest-hit northwest threatened to overwhelm a major dam and unleash a new deluge....