Allow overriding the plugged status of a port

Some users have broken jacks that do not report the plugged-in status. hdjackretask can work around this, but only on platforms with Intel HD Audio or compatible sound cards. This provides a general solution that works for all sound cards.

I used an environment variable because this is fairly deep in the code and I am not sure how to plumb a property there.

Signed-off-by: Demi Marie Obenour demiobenour@gmail.com