Horizon culling cleanup.

Mostly to match the forthcoming blog article.
Merge remote-tracking branch 'origin/master' into horizonCullingCleanup
merging with master
fixing 'undefined' bug
possible fix for #687
fixing animationcollection.js
fixing Billboard.js
fixing CameraController.js
fixing CustomSensoreVolume.js
fixing polyline.js and projections.js
fixing scenetransitioner.js
fixing rectangularpyramidsensorvolume
Merge pull request #1 from nobelium/checking

Explicitly checked for 'undefined'
Merge branch 'master' of github.com:nobelium/cesium
typo fixed in customsensorsvolume.js
used ternary operator if creating the second operand is expensive
Merging with Cesium/master
fixed unsuccessful merge bugs
Merge branch 'master' of github.com:AnalyticalGraphicsInc/cesium
Merge remote-tracking branch 'origin/master' into horizonCullingCleanup