speak() and speakUtterances() had the use of the interrupt argument
commented out back in 2007 due to unspecified issues. In 2013, we
enabled this and then immediately re-disabled it due to regressions.
Most of the code handles interruption via explicitly calling the
script's presentationInterrupt method which calls speech.stop,
which causes _cancel to be called in speechdispatcher factory. That
said, there may be downstream/external scripts/functionality that
for some reason isn't calling presentationInterrupt or stop. And
having this option in place but non functioning seems silly. So we'll
re-enable it but set the default value to False in the hopes that we
minimize the number of regressions that may be unexpectedly introduced
by this change.