As some PHC hardware/drivers don't provide PPS, it may be useful to keep the
system clock synchronized to PHC via clock_gettime(). While the precision
of the clock is only in microsecond range, the error seems to be quite stable.
The -d parameter now can be omitted if -s is provided.
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Richard Cochran