Summary: Big file cannot be opened via FDO provider

[stevenxu]

The behavior of system call _wstat in VC9 and VC10 is different when handling file which size is bigger than 2^{31. In VC9, it returns 0. But in VC10, it returns -1. Then some checks will be failed when opening a big file, which results in the big file cannot be opened in Map. To fix this issue, we need to use _wstat64 instead of _wstat.}