Updated core interface wrt settings sounds devices

- playback_devices and recording_devices properties now contain strings
  insteads of internal PJMEDIASoundDevice object
- set_sound_devices() now take strings as parameters in order to support
  persistent sound device names in configuration
- set_sound_devices() now take None as argument for sound devices to do
  automatic device selection
- auto_set_sound_devices() has been removed

darcs-hash:20090227105602-58103-e7c695c87b4fcb15e77dc4b16be4c069bb75dbcb