mounting issue

When dragging a component, I noticed that the component being dragged executes the `componentWillMount` method upon drag start. I believe that this would be a bug. The component shouldn't have to remount just to be dragged.

In my case, I have a component that does some heavy processing upon being mounted, therefore, when I try to sort components, there is some huge lag between pressing and dragging the selected component.

Start by reproducing the drag behavior described in the issue and trace the component lifecycle during drag start. Done means dragging does not trigger componentWillMount or an unnecessary remount, avoiding the reported lag for components with heavy mount processing.

Written by the indexing model from the issue text.