When Credicorp (BAP) soared 5.5% in the stock market Thursday, the heavy-volume gain helped improve its Accumulation/Distribution Rating to A- from B+. Credicorp normally trades close to 300,000 shares a day, but on Thursday volume more than doubled to 701,000 shares. IBD's Accumulation/Distribution Rating looks at a stock's price and volume over the past three months of trading. Heavy-volume up… ...