Workaround for: 'PFObject' does not have a member named 'subscript'

PFObjectSubscriptExtension.swift

// Workaround for Parse 1.6.4 and Xcode 6.3, see: http://stackoverflow.com/questions/28953306/pfobject-does-not-have-a-member-named-subscript/29015269#29015269
extension PFObject {
  subscript(index: String) -> AnyObject? {
    get {
      return self.valueForKey(index)
    }
    set(newValue) {
      if let newValue: AnyObject = newValue {
        self.setValue(newValue, forKey: index)
      }
    }
  }
}