'RELENG_6_0_0_RELEASE'.

This commit was manufactured to restore the state of the 6.0-RELEASE image.

Since they were never documented and have never appeared in a FreeBSD
release, no repo-copy of the header is done.  This removes namespace
pollution from <time.h>.

I believe have made all of libc .c's as consistent as possible.

time_to_xxx() and xxx_to_time() functions.  e.g. _time_to_xxx()
instead of time_to_xxx(), to make it more obvious that these are
stopgap functions & placemarkers and not meant to create a defacto
standard.  They will eventually be replaced when a real standard
comes out of committee.

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