swift234

Foundation overlay: Add a generic NSCoder.decodeObjectOfClass(_:forKey:).

Like decodeTopLevelObjectOfClass(_:forKey:), this API works very nicely
as a generic method in Swift, and this one is actually the one we expect
to be commonly used. One thing to note here is that these methods are
stricter than their ObjC counterparts: they will do a forced checked cast
even when the unarchiver does not use "secure" coding.

This depends on the previous commit; without it, we do not actually
enforce type safety for these methods.

The API notes change is to make the non-generic version of this method
unavailable so that it does not participate in overload resolution.
Without this we prefer the non-generic method unless there's a contextual
type for the result. I've filed rdar://problem/22243198 to track taking
this out once Foundation has updated their headers.

rdar://problem/17060110 (again)

Swift SVN r31154