Added `Scene.drillPick` for picking of multiple primitives
handle multiple ways of hiding primitives
changed test to check if setShow function is defined
fixed doc comment
Merge branch 'master' of https://github.com/gbeatty/cesium into multiPicking

Conflicts:
	CHANGES.md
	Source/Scene/Scene.js
first pass
working polyline volume
Merge branch 'master' into multiPicking

Conflicts:
	CHANGES.md
cleanup formatting
completed outline
Clear tracked object when data sources are removed.
sandcastle example, web workers
Merge branch 'master' into polylineVolume
specs
formatting
height WIP
fixed bad merge
code cleanup
sandcastle drill-down picking example
initial support for geometries