Extent.fromCartographicArray

The absense of this useful helper function became apparent during the International Space Apps Challenge.
Only set crossorigin on images that are actually cross-origin.

Cross-origin URLs are detected automatically by comparing the URL to the document location.
Merge pull request #685 from AnalyticalGraphicsInc/smarterCrossOriginImages

Only set crossorigin on images that are actually cross-origin.
Merge pull request #678 from AnalyticalGraphicsInc/extentFromCartographics

Extent.fromCartographicArray
Merge branch 'master' of github.com:AnalyticalGraphicsInc/cesium into checking
typo fixed in CustomSensorvolume.js