[Review] Add a Lazy flatMap for Sequences of Optionals

The review of SE-0015 “Tuple Comparison Operators" ran from December 21–22, 2015. The proposal has been accepted for Swift 2.2.

  swift-evolution/0015-tuple-comparison-operators.md at master · apple/swift-evolution · GitHub

Thank you to everyone who participated in the review process! A candidate implementation of this proposal, which may be merged pending evaluation, is at https://github.com/apple/swift/pull/408\.

-Dave