swift234

Improve handling of switch cases using nil literals when switching on an optional.

Now you can write:
switch nil as Int? {
  case let x?: break
  case nil: break
}
and this will generate code equivalent to using:

switch nil as Int? {
  case let x?: break
  case .None: break
}

This switch is exhaustive and no unreachable code is generated.

rdar://20130266

Swift SVN r26635