Force runtimes to handle x-domain. Explicit flag to indicate support

This is to resolve my issues on Issue #21.

Note: I kept with a simple check for CORS and didn't bother with XDomainRequest. If we incorporated XDomainRequest we could pick up IE 8 and 9 support but XDomainRequest has a bunch of odd restrictions (only plain text, only GET and POST, etc.). So I stuck with just browsers that support the latest standard. I figure IE 8 and 9 can fallback on Flash.