Picking coordinates on 2D mode: Middle-click rotation.

[DavidHudlow]

Steps:

1. Go to Sandcastle picking: http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Picking.html&label=Showcases
2. Replace line 504 with

var widget = new Cesium.CesiumWidget('cesiumContainer', { sceneMode : Cesium.SceneMode.SCENE2D }); 

to enable 2D mode
3. Middle-click on map and drag to rotate
4. Continue picking.

Expected result: Picking should display coordinates in the same place relative to the pointer and should correspond to the location of the pointer relative to the map.

Actual result: Display of coordinates wanders from the mouse pointer and displays coordinates accordingly.

[pjcozzi]

@bagnell can you verify this and see if there is a workaround?

[bagnell]

This is fixed in the above pull, but picking is still broken when the map is rotated. I'll open a separate issue for it.