This pull request is for Windows only so we should only be concerned with how VS2010 treats the data type for the moment. I'm not sure how file systems on other platforms treat exceptionally large files but, I think for Windows, a double should be sufficient.  I'm also not certain what the final usage of this functionality is but, as I mentioned before, files that approach Number.MAX_VALUE are not going to be usable in brackets anyway. So, other than reporting, it may not matter much what value is returned for exceptionally large files.

I was hoping `long double` was implemented on x86 but it only appears to be only implemented in Intel C++ Compilers and some flavors of GNU C++ Compilers.