Pull up following revision(s) (requested by thorpej in ticket #651):

sys/dev/usb/ugen.c: revision 1.177

ugen and ugenif share the same /dev/ugenN.xx namespace in such a way
that the device unit number does not necessarily match the /dev/ugenN.xx
unit number (N).  If you ONLY have ugen devices, it happens to work out
and devpubd scripts can be extremely naive.  If you ONLY have ugenif
devices, it also happens to work out, but your devpubd scripts have to
slightly more informed.  If you have a mix of ugen AND ugenif devices,
though, you're pretty much out of luck.

So, this change adds a "ugen-unit" device property which devpubd scripts
can query to determine which /dev/ugenN.xx nodes a given ugen or ugenif
device is using.

(martin)