Fixed handling of audio.silent general setting

Ignore-this: 60fcdd89eb26f38481300e5e293a41be

darcs-hash:20090824140903-1e3d8-e6f50d80ff88aefd80cd6a8256cb15e7bca39753
Added handling of changes to settings in SIPApplication

Ignore-this: c8e0dedeaf00cf97d98b2b4f4446ba10

darcs-hash:20090824155318-1e3d8-2b481368aa34828328404c111342713e1853916c