* bus_setup_intr() as a wrapper for BUS_SETUP_INTR
* bus_teardown_intr() as a wrapper for BUS_TEARDOWN_INTR
* device_get_nameunit() which returns e.g. "foo0" for name "foo" and unit 0.
* device_set_desc_copy() malloc a copy of the description string.
* device_quiet(), device_is_quiet(), device_verbose() suppress probe message.
Add one method to the BUS interface, BUS_CHILD_DETACHED() which is called
after the child has been detached to allow the bus to clean up any memory
which it allocated on behalf of the child.
I also fixed a bug which corrupted the list of drivers in a devclass if
a driver was added to more than one devclass.