[PATCH] Make usb bus enumeration work reliably

Attached patch fixes the way how the usb busses/devices are enumerated by libusb. It changes it to use the dirname/filename string members instead of the numeric location/devnum members.

It appears the numerical members change among consecutive calls and are not reliable. When testing it even reported all bus->location members to be 0 for ALL devices and busses which of course leads to problems when using iphone_get_specific_device().

Looking at other projects sources reveals that the only reliable way is to parse the dirname/filename strings and use them to determine a bus/device combination.

All this ofc. unless I have overlooked some other "sync-kind" of call for libusb, but judging from the other sources this is the way it is supposed to be done.