swift234

Import Objective-C properties marked weak/copy as weak/@NSCopying.

...and 'assign' and 'unsafe_unretained' as 'unowned(unsafe)', if the
property is a class type.

This isn't important for the compiler, but it is documentation for users
when they look at the generated interface for an Objective-C module.

Note that this actually produces a decl users can't yet write:

  unowned(unsafe) var foo: UIView!

That's <rdar://problem/17277899> unowned pointers can't be optional.

<rdar://problem/17245555>

Swift SVN r20433