Improves payload type overriding for SIP/XMPP so that it would remove payload type overrides when necessary.

src/net/java/sip/communicator/impl/protocol/sip/sdp/SdpUtils.java

@@ -166,7 +166,7 @@ public static SessionDescription createSessionDescription(
 
             //o
             if (userName == null)
-                userName = "sip-communicator";
+                userName = "jitsi.org";
 
             Origin o = sdpFactory.createOrigin(
                 userName, 0, 0, "IN", addrType, localAddress.getHostAddress());

src/net/java/sip/communicator/service/protocol/media/DynamicPayloadTypeRegistry.java

@@ -243,7 +243,10 @@ public void addMapping(MediaFormat format, byte payloadType)
             if(alreadyMappedFmt.matches(format))
             {
                 //we already have the exact same mapping, so no need to
-                //create a new one override the old PT number.
+                //create a new one override the old PT number. However, there
+                //might be a leftover override from a previous mapping so let's
+                //remove it if this is the case.
+                payloadTypeOverrides.remove(payloadType);
                 return;
             }
             //else: