title: NSCalendarUnitDay shows the current day as a single digit int. How can I make it 2 digits such as "03"?
body: <p>So I'm creating a date string in MMyy format:</p>
  
  <pre><code>        var components: NSDateComponents!
          components = calendar.components(.CalendarUnitYear | .CalendarUnitMonth | .CalendarUnitDay, fromDate: NSDate()) as NSDateComponents
          let stringDate = "\(components.month)\(components.day)" // "113"
  </code></pre>
  
  <p>If a day is less than 10 then I get a 3 digit number as a string. </p>
  
  <p>How do I change things so that I get a 4 digit number as a string instead e.g. "1103"?</p>