Include the response message in the error when postMessage fails.
Remove error property from DeveloperError and RuntimeError.

Errors can't be sent back from Web Workers.  We can still capture the stack trace as a string and use that, without the error object.
Add error property removal to CHANGES.
Merge pull request #1041 from AnalyticalGraphicsInc/fixExceptionsFromWebWorkers

Remove error property from DeveloperError and RuntimeError.