Call the listeners if a new ack might need to be sent.

api/net/sf/briar/api/db/DatabaseListener.java

@@ -4,6 +4,7 @@ package net.sf.briar.api.db;
 public interface DatabaseListener {
 
 	static enum Event {
+		ACKS_ADDED,
 		CONTACTS_UPDATED,
 		MESSAGES_ADDED,
 		SUBSCRIPTIONS_UPDATED,

components/net/sf/briar/db/DatabaseComponentImpl.java

@@ -937,6 +937,7 @@ DatabaseCleaner.Callback {
 			contactLock.readLock().unlock();
 		}
 		// Call the listeners outside the lock
+		callListeners(Event.ACKS_ADDED);
 		if(anyAdded) callListeners(Event.MESSAGES_ADDED);
 	}