s/gsh_time_t/struct timespec/g;

The gsh_time_t type is not usefully distinct from a POSIX timespec
structure.  Therefore, we should just use struct timespec.  For
consistency, rename members of XDR wire times which were shadowing
that structure.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>