Work around cross-origin Web Worker problems.

You can't create a Worker with a cross-origin URL, but you can create a Worker from a Blob URL containing a string which uses importScripts() to load that very same cross-origin URL.  Now, to me, this means you ought to just be able to create a Worker directly from a cross-origin URL, but I don't write the spec.
Specify MIME type for blobs
Update CHANGES.md
Fix Worker creation when loading AMD modules cross-origin too.
Fix Blob detection for older browsers.
Replace blob logic with try catch.
Merge pull request #633 from AnalyticalGraphicsInc/crossOriginWebWorker

Work around cross-origin Web Worker problems.
Merge branch 'master' into helloWorld