Fix errors and warnings on Xcode 6.1 / iOS 8.1

The original code was raising 12 compile-time errors:
`Type 'CFStringRef' does not conform to protocol 'NSCopying'`
    
I have fixed the errors as described here: http://swift-language.2336117.n4.nabble.com/CFString-does-not-conform-to-protocol-NSCopying-td116.html    

Also fixed is a warning about building for active architectures only in Xcode which was bugging me :)