Using forgotten id breaks gnuradio-companion

Hi

One of my flowgraph was generating the error:

    self.audio_sink_0 = audio.sink(audio_rate, '', True)
    AttributeError: 'int' object has no attribute 'sink'

This error was not easy to debug since the error message sounds like
there was a library error (which was not the case here).

My mistake was a "QT GUI Chooser" whose id was (incorrectly) set to
audio; "audio" being also the name of a gnuradio python module.

Now that I found my mistake, it's obvious that no ID should be set to
some python module name.

May be it could be interesting that gnuradio-companion tests block ids
and rejects forbidden ones when compiling flowgraph.

Regards