swift234

Teach isBridgedToObjectiveC and bridgeToObjectiveC to unwrap implicitly unwrapped optionals.

This allows us to, for example, convert an array of unchecked
optionals of some bridged type T to NSArray. It's a runtime failure if
the unchecked optional contains nil.

This is most of <rdar://problem/16899681>, but I want to improve the
testing and look into the various FIXMEs.


Swift SVN r18106