Import OpenBSD's sysctl hardware sensors framework.

This commit includes the following core components:

 * sample configuration file for sensorsd
 * rc(8) script and glue code for sensorsd(8)
 * sysctl(3) doc fixes for CTL_HW tree
 * sysctl(3) documentation for hardware sensors
 * sysctl(8) documentation for hardware sensors
 * support for the sensor structure for sysctl(8)
 * rc.conf(5) documentation for starting sensorsd(8)
 * sensor_attach(9) et al documentation
 * /sys/kern/kern_sensors.c
   o sensor_attach(9) API for drivers to register ksensors
   o sensor_task_register(9) API for the update task
   o sysctl(3) glue code
   o hw.sensors shadow tree for sysctl(8) internal magic
 * <sys/sensors.h>
 * HW_SENSORS definition for <sys/sysctl.h>
 * sensors display for systat(1), including documentation
 * sensorsd(8) and all applicable documentation

The userland part of the framework is entirely source-code
compatible with OpenBSD 4.1, 4.2 and  -current as of today.

All sensor readings can be viewed with `sysctl hw.sensors`,
monitored in semi-realtime with `systat -sensors` and also
logged with `sensorsd`.

Submitted by:	Constantine A. Murenin <cnst@FreeBSD.org>
Sponsored by:	Google Summer of Code 2007 (GSoC2007/cnst-sensors)
Mentored by:	syrinx
Tested by:	many
OKed by:	kensmith
Obtained from:	OpenBSD (parts)

1 files changed, 7 insertions, 0 deletions

diff --git a/usr.bin/systat/systat.1 b/usr.bin/systat/systat.1
index 0c5c4b5691ef..409d8bf6535d 100644
--- a/usr.bin/systat/systat.1
+++ b/usr.bin/systat/systat.1
@@ -101,6 +101,7 @@ to be one of:
 .Ic mbufs ,
 .Ic netstat ,
 .Ic pigs ,
+.Ic sensors ,
 .Ic swap ,
 .Ic tcp ,
 or
@@ -286,6 +287,11 @@ Areas known to the kernel, but not in use are shown as not available.
 .It Ic mbufs
 Display, in the lower window, the number of mbufs allocated
 for particular uses, i.e., data, socket structures, etc.
+.It Ic sensors
+Display, in the lower window,
+the current values of available hardware sensors,
+in a format similar to that of
+.Xr sysctl 8 .
 .It Ic vmstat
 Take over the entire display and show a (rather crowded) compendium
 of statistics related to virtual memory usage, process scheduling,
@@ -607,6 +613,7 @@ For port names.
 .Xr udp 4 ,
 .Xr gstat 8 ,
 .Xr iostat 8 ,
+.Xr sysctl 8 ,
 .Xr vmstat 8
 .Sh HISTORY
 The