Extent.fromCartographicArray

The absense of this useful helper function became apparent during the International Space Apps Challenge.
Fix to properly check for undefined values
Only set crossorigin on images that are actually cross-origin.

Cross-origin URLs are detected automatically by comparing the URL to the document location.
Fix formatting for define
Fix to properly check for 'undefined'
Fix to properly check for 'undefined' and default value initializations
Merge pull request #685 from AnalyticalGraphicsInc/smarterCrossOriginImages

Only set crossorigin on images that are actually cross-origin.
Fix to properly check for 'undefined'
Fix to properly check for 'undefined'
Fix to properly assign a default value
Fix to properly check for 'undefined'
Merge pull request #678 from AnalyticalGraphicsInc/extentFromCartographics

Extent.fromCartographicArray
Fix to properly check for 'undefined' and assign default values
Merge pull request #684 from andre-nunes/issue89

Fix to properly check for 'undefined'
Fix my botched pull request merge.
used ternary operator if creating the second operand is expensive
Merging with Cesium/master