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
Merge branch 'master' into multiPicking

Conflicts:
	CHANGES.md
fixed bad merge
code cleanup
sandcastle drill-down picking example
initial support for geometries
removed unused require
Merge branch 'master' into multiPicking

Conflicts:
	CHANGES.md
correctly handle geometry picking
Removed prototype for toArray from Matrix2/3/4
Removed prototype for get/setColumn from Matrix2/3/4
Removed prototype for get/setRow from Matrix2/3/4
Removed prototype for multiply, multiplyByVector, and multiplyByScalar from Matrix2/3/4
Removed prototype for equals and equalsEpsilon from Matrix2/3/4
Removed prototype for negate and transpose from Matrix2/3/4
Removed prototype for getTranslation and getRotation from Matrix4