ACPI: Battery hotplug support

Hi, all,

This patch series is for battery hotplug support. Please refer to http://bugzilla.kernel.org/show_bug.cgi?id=2884

Patch 01 flushes kacpi_notify_wq before removing the notify handler
as well as the kacpid_wq.
Patch 02 adds a new acpi execute type, OSL_DEVICE_HOTPLUG_HANDLER,
This is used for the device hotplug notify handler which will be queued in keventd_wq so that it can flush the kacpi_notify_wq.
Patch 03 support battery hotplug in the global system-level notify handler
acpi_bus_notify.
Patch 04 fix the deadlock when pokiing the "eject" sysfs attribute
which is used to eject a device in user space.

I've tested this patch set on my t43 laptop and it works well. Any comment is appreciated. :)

Thanks,
Rui

Series applied to acpi-test

thanks,
-Len