swift234

Update for feedback from Dmitri.

Simplify the observation evaluation in the ErrorType race test by using evaluateObservationsAllEqual, and run the test for real. Apparently round-trip NSString and NSDictionary bridging doesn't produce a stable object, so use valueForKey as a hack to sidestep bridging so we can verify that the identities of the bridged domain and code aren't racy.

Swift SVN r27003