factory methods avoid creating unnecessary temporaries

Avoid some ref. counter activity (still have global mutex...)

src/factory/FieldCreateFactory.cpp

@@ -1418,7 +1418,7 @@ FieldConstPtr FieldCreate::deserialize(ByteBuffer* buffer, DeserializableControl
 }
 
 // TODO replace with non-locking singleton pattern
-FieldCreatePtr FieldCreate::getFieldCreate()
+const FieldCreatePtr& FieldCreate::getFieldCreate()
 {
 	LOCAL_STATIC_LOCK;
 	static FieldCreatePtr fieldCreate;
@@ -1456,10 +1456,6 @@ FieldCreate::FieldCreate()
     variantUnionArray = sua;
 }
 
-FieldCreatePtr getFieldCreate() {
-    return FieldCreate::getFieldCreate();
-}
-
 }}
 
 namespace std{