title: Swift app crashes on real device but works on simulator
body: <p>This function gets the date from yesterday; it is working on my emulator but it crashes with my real device.</p>
  
  <p>I am working with Xcode6 Beta 6.</p>
  
  <pre><code>var tuple :(value Int, unit:NSCalendarUnit) = (1, NSCalendarUnit.CalendarUnitDay)
  var date = NSDate()
  var yesterday = NSCalendar.currentCalender().dateByAddingUnit(tuple.unit, value: (-tuple.value), toDate: date, options: NSCalendarOptions.SearchBackwards)
  </code></pre>
  
  <p>This is the error I get on my real device:</p>
  
  <pre><code>-[_NSCopyOnWriteCalendarWrapper dateByAddingUnit:value:toDate:options:]: unrecognized selector sent to instance 0x176cca10
  </code></pre>