[IronPython] Importing on another Thread

[Jimmy Schementi]

> DynamicApplication.DownloadContents eventually
> calls Application.GetResourceStream, which will throw if on a
> background thread.

Note: DownloadContents is actually a misleading name, since it doesn't download anything; it just looks in the XAP for them. Those "Download" methods on DynamicApplication will be renamed in the future.

~Jimmy