swift234

Diagnose Objective-C conflicts due to unsatisfied, optional @objc requirements.

An optional @objc requirement within a protocol can be left
unsatisfied in a well-formed program. However, there may still be a
conflict within the Objective-C runtime if the conforming class
defines a method with the corresponding Objective-C selector(s) for
that requirement, which means that the Swift and Objective-C semantics
will differ. Diagnose such issues.

More steps along the road to fixing rdar://problem/18383574.

Diagnose conflicts between unsatisfied, optional @objc requirements and

Swift SVN r24830