feature: allow to disable the call to jack_connect

[ycollet]

I use Audacity / Jack on Fedora via the portaudio driver.
I am not able to deactivate the auto-connexion from Jack (performed via jack_connect).

I was wondering if it was possible to disable the call to jack_connect here:

portaudio/src/hostapi/jack/pa_jack.c

Line 1702 in adbf810

if( stream->num_incoming_connections > 0 )

via an environment variable ?

And via such a call:

PA_DISABLE_JACK_CONNECT=1 audacity

The automatic connections will be disabled ...