Swift 2 compatibility

[Bryan Anderson]

Getting the error "'find' is unavailable: call the indexOf() method on the collection" on this portion of code:

    func indexOf <U: Equatable> (item: U) -> Int? {
    if item is Element {
        return Swift.find(unsafeBitCast(self, [U].self), item)
    }

    return nil
}

[Takuma Yoshida]

Thank you for your issue! I created swift-2.0 branch.