Added permanent references to AudioStream to keep pjsip from crashing

Ignore-this: 44ad52a60f77bc1b1c6469d805db066f

darcs-hash:20100511173424-1e3d8-2531580bf6b3e28fcc068db03f0c985f6555d414
Modified AudioMixer so that it keeps the sound device open on Mac OS X 10.6

Ignore-this: 96ddd4f71740aa3578a626060b7402be

darcs-hash:20100511173749-1e3d8-526a52415b74d5529d93b95d62b149b72e7bb0b0