to shut down; close laptop lid" scenario which otherwise tended to end
with a laptop overheating or the battery dying.
The implementation uses a new sysctl, kern.suspend_blocked; init(8) sets
this while rc.suspend runs, and the ACPI sleep code ignores requests while
the sysctl is set.
Discussed on: freebsd-acpi (35 emails)
MFC after: 1 week
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