core, memory, plugins, stdui, frontends: look for DNS SRV records when server is not specified:

- fix bug 3
    - modify "Connection" params:
          - rename "Server" to "Force server" and "Port" to "Force port"
          - set the default value to empty string for both

src/core/xmpp.py

@@ -37,7 +37,9 @@ class SatXMPPClient(client.XMPPClient):
     implements(iwokkel.IDisco)
 
     def __init__(self, host_app, profile, user_jid, password, host=None, port=5222):
-        client.XMPPClient.__init__(self, user_jid, password, host, port)
+        # XXX: DNS SRV records are checked when the host is not specified.
+        # If no SRV record is found, the host is directly extracted from the JID.
+        client.XMPPClient.__init__(self, user_jid, password, host or None, port or 5222)
         self.factory.clientConnectionLost = self.connectionLost
         self.__connected = False
         self.profile = profile