FreeBSD (and other systems as well) may use libusb to work with USB devices.
libusb is integrated in FreeBSD base system in recent builds (8.0+),
however in other systems it may need include libusb.h like <libusb/libusb.h>
and install library from devel/libusb port or other repository.
Submitted change not supports events (attach/detach) as libusb 1.0 lacks
such functionality and in order to make code more portable I've not used
workarounds as in earlier changeset.
Code was tested on FreeBSD 8.0-RC1, HTC Hero (1.0.0.A6288, Android 1.5)
Added usb_vendors.* which handles creating (and deleting) a list of vendor ids.
This list is meant to be used everywhere the built-in lists (usb_osx), or the
built-in vendor IDs (transport_usb) were used.
For now the list is only built with the built-in VENDOR_ID_*. Next step
is to read a small file created from all the SDK add-on.
Other misc changes: made is_adb_interface present only if ADB_HOST is true
to prevent accessing a list that doesn't exist (usb_vendors is only
compiled for the host version of adb).
