hdf5_ep

[svn-r9440] Purpose:
Bug fix

Description:
Fix typo in #ifdef for unsigned long long to double conversion.
Changed WIN32 check to H5_ULLONG_TO_FP_CAST_WORKS
This check-in (and the one before it) also includes a large code-refactoring
that is still in progress.

Solution:
the ifdef for the plus case was checking unsigned long instead of unsigned
long long.  Moved the check to the right location.

Platforms tested:
sol+eirene

Misc. update: