We have found in the course of hacking on HAL that some information that
is in /proc/bus/usb/devices is not in sysfs.  It would be nice to rely
only on sysfs, so the attached patch adds three files to usb devices in
sysfs: devnum, maxChild, and version.

This patch is actually by David Zuethen, the HAL maintainer - I told him
I would clean it up and get it upstream.