Promise synchronous polling

[johnhaley81]

I was wondering if I could change Promise to support something like bluebird's synchronous inspection. This would allow the user to inspect a promise to see if it's resolved and would not let them modify any internal values.

Originally I was going to do this as an extension but I think that'd I'd have to modify the lib/core.js file to really support this. I'd be willing to write this myself, it wouldn't be difficult.

[ForbesLindesay]

I'm not sure if we should add that functionality to an intentionally minimal implementation. It is, in general, a footgun that makes it much easier to create code that relies on race conditions.

[johnhaley81]

I was thinking about doing it as an extension originally, but the way that it's implemented makes it pretty awkward to do this.