vchoi_fork

[svn-r9172] Purpose:
"bug fix" sort of.

Description:
The current mpicc at TG-NCSA recognizes uint64_t but not
int64_t.  hdf5 code rightly assumes when the unsigned type
is defined, the corresponding signed type should be valid
too.  So, when it detected uint64_t is valid, it went ahead
using int64_t which ended in compiling failure.

Solution:
Changed the detection to check on int64_t instead.  This does
not change any logic, just goes around the mpicc compiler error
at TG-NCSA.

Platforms tested:
h5committested and tested at TG-NCSA (pp) too.

Misc. update: