- gnuradio-companion needs to be invoked with root privilege
  if you add several input devices, say, to activate following parts 
         Sources -> RTL-SDR Source
                    osmoscom Source
  etc. One way to to this is (as my example)
  X11 -> xterm -> sudo -s 
      -> export XAUTHORITY=/home/my_login/.Xauthority
      -> gnuradio-companion
  (Thanks rkujawa@ for this)
  
- OPTIONS.gnuradio= ninja doesn't package with error:
  # Adding ninja to following line (now) stops
  # [164/850] cd /PATH/wip/gnuradio-core/work/gnuradio-3.7.5/build/gr-audio/swig && ""
  # FAILED: cd /PATH/wip/gnuradio-core/work/gnuradio-3.7.5/build/gr-audio/swig && ""
  # : permission denied
  (updating cmake 3.0.2 in wip doesn't help)

