if random number is initialized to 0, it will be reset on next run()

[jauboux]

generateRandomNumber() return a number in [0,99]
stored integer is tested against 0 so there is 1 chance out of 100 that number will change:

    public func ab_getRandomNumberWithKey(key: String) -> Int {
        var randomNumber = integerForKey(key)
        if randomNumber == 0 {
            randomNumber = generateRandomNumber()
            setInteger(randomNumber, forKey: key)
        }
        return randomNumber
    }