Dispose of IRCConnections properly to avoid leaking IRCService objects

Each IRCConnection starts an input thread and an output thread when
created; if not stopped, these threads continue to hold the IRCService,
resulting in a leak when the service is stopped.  Fix this by using
PircBot's dispose() to stop the threads when disposing of the
IRCConnection.

application/src/org/yaaic/irc/IRCService.java

@@ -372,7 +372,14 @@ public class IRCService extends Service
         for (int i = 0; i < mSize; i++) {
             server = mServers.get(i);
             if (server.isDisconnected()) {
-                connections.remove(server.getId());
+                int serverId = server.getId();
+                synchronized(this) {
+                    IRCConnection connection = connections.get(serverId);
+                    if (connection != null) {
+                        connection.dispose();
+                    }
+                    connections.remove(serverId);
+                }
             } else {
                 shutDown = false;
             }