Merge change I0f73439a into eclair

* changes:
  Partially fix bug 2111240 Detect docking / undocking event by reporting to the AudioPolicyManager a new forced usage AudioSystem::FOR_DOCK which can take the FORCE_NONE, FORCE_BT_DOCK or FORCE_WIRED_ACCESSORY values. This CL is complemented by an update of the APM to take into account the FOR_DOCK usage.