Merge branch 'libusb-1.0' of git://github.com/ttsou/gnuradio-ttsou

This merge fixes libusb build machinery to work for Cygwin, Darwin, Ubuntu,
and F11.

* 'libusb-1.0' of git://github.com/ttsou/gnuradio-ttsou:
  usrp: Applied patch from Michael Dickens for Darwin libusb
  usrp: Applied patch from Don Ward for Cygwin libusb
  fix to restart libusbok checking for non-PKGCONFIG
  usrp: Disabled libusb-1.0 debug output by default
  merged updated libusb checks with older version
  usrp: Enable debug output
  usrp: Reorg of libusb error reporting
  usrp: Added error checking on hash transfers
  augmented search for libusb