Descriptor for a class defined in another module of THIS assembly and exported (.class extern)
Inheritance: Class
		public ClassRef AddNestedClass(TypeAttr attrs, string name) 
		{
			ExternClassRef nestedClass = new ExternClassRef(name,metaData);
			externClass = new ExternClass(attrs,0,nameIx,this.externClass);
			metaData.AddToTable(MDTable.ExportedType,externClass);
			return nestedClass;
		}
		internal ExternClassRef(TypeAttr attrs, string nsName, string name,
				FileRef declFile, MetaData md) : base(nsName,name,md) 
		{
			externClass = new ExternClass(attrs,nameSpaceIx,nameIx,declFile);
			metaData.AddToTable(MDTable.ExportedType,externClass);
		}