MFC 238424:

MFC 238424:
Make the interval timings for EVFILT_TIMER more accurate.  tvtohz() always
adds an extra tick to account for the current partial clock tick.  However,
that is not appropriate for a repeating timer when the exact tvtohz() value
should be used for subsequent intervals.  Fix repeating callouts for
EVFILT_TIMER by subtracting 1 tick from the tvtohz() result similar to the
fix used in realitexpire() for interval timers.

While here, update a few comments to note that if the EVFILT_TIMER code
were to move out of kern_event.c, it should move to kern_time.c (where the
interval timer code it mimics lives) rather than kern_timeout.c.

git-svn-id: svn://svn.freebsd.org/base/stable/8@239916 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f