Right now, only power switch state change events are supported. This
is a work-in-progress.
* Add support to sysmon for delivering power mangement events to userland.
Add poll, kqueue, and read entry points to sysmon.
* Adapt ACPI to use the new generic <sys/power.h> event types.
This provides the kernel support for a forthcoming powerd(8) which can
do nice things like gracefully shut the system down when an ACPI power
button is pressed.
thorpej