title: libusb-1.0 debug informations
body: <p>I’m wondering if libusb_set_debug() works. I can’t get any output from it.
  I can turn on debug logging if I configure and build with --enable-debug-log.
  Should I get about the same output as enable-debug-log if I set libusb_set_debug() to 3?
  I don’t have the LIBUSB_DEBUG env variable set.
  I assume I’m missing something simple.
  Thanks,</p>