MFcalloutng:
kern_nanosleep() is now converted to use tsleep_sbt(). With this change
nanosleep() and usleep() can handle sub-tick precision for timeouts.
Also, try to help coalesce of events passing as argument to tsleep_bt()
a precision value calculated as a percentage of the sleep time.
This percentage is default 5%, but it can tuned according to users
need via the sysctl interface.

Sponsored by:	Google Summer of Code 2012, iXsystems inc.
Tested by:	flo, marius, ian, markj, Fabian Keil
MFcalloutng (r244255 by mav, with minor changes):
Specify that syslog doesn't need exactly 5 wakeups per second.

Sponsored by:	Google Summer of Code 2012, iXsystems inc.
Tested by:	flo, marius, ian, markj, Fabian Keil
MFcalloutng (r236314 by mav):
Specify that wakeup rate of 7.5-10Hz is enough for yarrow harvesting
thread.

Sponsored by:	Google Summer of Code 2012, iXsystems inc.
Tested by:	flo, marius, ian, markj, Fabian Keil
MFcalloutng (r244251 with minor changes):
Specify that precision of 0.5s is enough for resource limitation.

Sponsored by:	Google Summer of Code 2012, iXsystems inc.
Tested by:	flo, marius, ian, markj, Fabian Keil