This decreases total testing time by over a minute on my old Mac Pro.
It probably has much less effect on systems with fewer cores, but shouldn't
be any worse there.
Swift SVN r22745
UIViewController is able to find nib files that have names derived from the
UIViewController subclass's name. This change modifies UIViewController's
lookup so it is able to find nib files for Swift class names.
Swift SVN r18470