Mantis #7514

Mono bug introduces double xmlns attribute names when rewriting the asset in HGAssetService, e.g.  <SceneObjectPart xmlns:xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xmlns:xsd="http://www.w3.org/2001/XMLSchema">.
Solution: remove all attributes before saving.

OpenSim/Framework/Serialization/External/ExternalRepresentationUtils.cs

@@ -136,6 +136,9 @@ namespace OpenSim.Framework.Serialization.External
 
             foreach (XmlNode sop in sops)
             {
+                // Due to mono bug, we're removing all xmlns attributes
+                sop.Attributes.RemoveAll();
+
                 UserAccount creator = null;
                 bool hasCreatorData = false;
                 XmlNodeList nodes = sop.ChildNodes;