Changed osgAnimation::StackedTransform::update(t). It can now be used for custom usage

src/osgAnimation/StackedMatrixElement.cpp

@@ -33,7 +33,7 @@ Target* StackedMatrixElement::getOrCreateTarget()
     return _target.get(); 
 }
 
-void StackedMatrixElement::update()
+void StackedMatrixElement::update(float t)
 {
     if (_target.valid())
         _matrix = _target->getValue();