serve two purposes: (1) so we can maintain backwards compatibility with
protocols (rwhod, dump, etc...) that either assume time_t is 32 bits or
assume sizeof(time_t) == sizeof(int), or make other similar assumptions.
(2) To tag such routines (by the presence of these calls) for future
cleanup/extension work.
The 32->64 routine, time32_to_time() (when time_t is 64 bits, that is),
is defined specifically to implement temporal locality to properly set the
msb bits of a 64 bit time_t quantity, using the 50 year rule. The locality
code has not been implemented yet (and doesn't need to be for a while),
but that is the intent. This will allow us to maintain backwards protocol
compatibility past 2038.
These routines are intended to be platform and time_t agnostic.
MFC after: 1 week
5b521f3c4f