Update ExcelFile.as

We found a problem when reading the value 0.015 from an Excel file. It was read as 0.02 (whereas 0.016 was read correctly, as was 0.01501). The function readRK() was not masking bits 30 & 31 (RK format has only 30 significant bits) and was also rounding when dividing by 100.

Also see https://code.google.com/p/as3xls/issues/detail?can=2&start=0&num=100&q=&colspec=ID%20Type%20Status%20Priority%20Milestone%20Owner%20Summary&groupby=&sort=&id=64