factory methods avoid creating unnecessary temporaries

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

src/factory/StandardField.cpp

@@ -644,7 +644,7 @@ StructureConstPtr StandardField::enumeratedAlarm()
     return enumeratedAlarmField;
 }
 
-StandardFieldPtr StandardField::getStandardField()
+const StandardFieldPtr &StandardField::getStandardField()
 {
     static StandardFieldPtr standardFieldCreate;
     static Mutex mutex;
@@ -658,10 +658,4 @@ StandardFieldPtr StandardField::getStandardField()
     return standardFieldCreate;
 }
 
-
-
-StandardFieldPtr getStandardField() {
-    return StandardField::getStandardField();
-}
-
 }}