Implement API to have new broadcasts replace existing broadcasts.

Use this in various places where it should serve no purpose to deliver
both broadcasts.  This is intended to reduce somewhat the flurry of
broadcasts that we churn through during boot.

services/java/com/android/server/DockObserver.java

@@ -179,6 +179,7 @@ class DockObserver extends UEventObserver {
                 }
                 // Pack up the values and broadcast them to everyone
                 Intent intent = new Intent(Intent.ACTION_DOCK_EVENT);
+                intent.addFlags(Intent.FLAG_RECEIVER_REPLACE_PENDING);
                 intent.putExtra(Intent.EXTRA_DOCK_STATE, mDockState);
 
                 // Check if this is Bluetooth Dock