Don't access AudioOutput::pause.

Don't access AudioOutput::pause.

This allows removing the "base.pause" check from the JACK output
plugin, and will allow removing similar accesses from other plugins.

Prepare to move some configuration settings from AudioOutput to
AudioOutputControl.

We can remove those C++11 and C++14 kludges because we require GCC 4.9
now.

Fixes build failure on OS X, closes #44.  With the other plugins,
that's not critical, because those use the AudioOutputWrapper, which
hides this problem.