Improved audio device handling in SIPApplication

Ignore-this: c7efb2f5d47acc3523259477f6aadd5b

darcs-hash:20100115123620-1e3d8-4c28d76ff430a7eba7e83cb33f0f02e8865377df
End session if 408 or 481 was received for re-INVITE (RFC 3261, sec. 14.1)

Ignore-this: a2fc9d04c2f5715cd51bea5575335335

darcs-hash:20100115131803-56b4d-fae4fe9679e1e79ac92e8023c3ebf2a22e86af9d