Added automatic fallback to previously selected audio device

Ignore-this: 3569a44ad4f468767df7b94abcb52b0d

darcs-hash:20130505101254-58252-1622590f0da6f2365153fcf1c97bc683ca9fa2e0
Return SIP Request headers in SIPMessageDidFail and SIPMessageDidSucceed notification data

Ignore-this: d0c5805296336446c92136cc25ed7f5d

darcs-hash:20130509081420-58252-2a6da8a9c018962d8e5a382d4371fdc56095aaf2