SMACK-458 Managers should be kept on disconnects

Smack's Managers should not remove itself when the connection is closed
or should re-add themselves if the connection get reconnected.

This should also fix some NPE's.

We are currently going with two different designs of Manager: 1. The one
with WeakReferences/WeakHashMaps (SDM, EntityCapsManager) and 2. the one
where the managers remove their listeners on connectionClosed() *and*
connectionClosedOnError(), and later add their listeners on
reconnectionSuccessful(). The first design has the Connection instance
only weak referenced. The other design does reference Connection
strongly (e.g. the 'managers' map in IBBManager/S5BManager), but removes
this references when connectionClosed(onError)() is called.

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/branches/smack_3_3_2@13788 b35dd754-fafc-0310-a699-88a17e54d16e

test-unit/org/jivesoftware/smackx/filetransfer/FileTransferNegotiatorTest.java

@@ -39,7 +39,7 @@ public class FileTransferNegotiatorTest {
         connection = new DummyConnection();
         connection.connect();
         connection.login("me", "secret");
-        new ServiceDiscoveryManager(connection);
+        ServiceDiscoveryManager.getInstanceFor(connection);
     }
 
     @After