added ability to replace existing entries in a LLRegistry

indra/llxuixml/llregistry.h

@@ -76,6 +76,11 @@ class LLRegistry
 			mMap.erase(key);
 		}
 
+		void replace(ref_const_key_t key, ref_const_value_t value)
+		{
+			mMap[key] = value;
+		}
+
 		typename registry_map_t::const_iterator beginItems() const
 		{
 			return mMap.begin();