Compile if libusb doesn't have libusb_error_name

The API function libusb_error_name was introduced in libusb v1.0.9. We want to
compile on versions older (for example ubuntu lucid). So detect whether
function is present and implement workaround if it is not.

Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>
Reduce debug level of USB ignore messages

Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>