title: Date picker shows a different date (1 day behined) from when picked
body: <p>I have a UIDatePicker that is connected to a UILabel. I want the user to pick a birthday that is more than 18 years ago (age restriction). So I have this line to set the <code>maximumDate</code> value: </p>
  
  <pre><code>datePicker.maximumDate = NSCalendar.currentCalendar().dateByAddingUnit(.Year, value: -18, toDate: NSDate(), options: [])
  </code></pre>
  
  <p>This line however causes the picker to show a 1 day behind the selected date. for example if I choose <code>September 27, 1956</code> on the picker the label shows <code>September 26, 1956</code> I believe it has to do with <code>NSDate()</code> using a different timezone one that is behind my local timezone. </p>
  
  <pre><code>switch dequeueFrom[indexPath.row] {
      case .Birthday:
          if let pickedBday = pickedBday,
          let bday = NSDate.dateFromISOString(pickedBday) {
              (cell as! RegisterTextFieldCell).content(bday.longFormattedString())
          }
  </code></pre>
  
  <p><code>// dateFromISOSString is declared in an extension.swift</code></p>
  
  <pre><code>class func dateFromComponents(components: NSDateComponents) -&gt; NSDate? {
      let calendar = NSCalendar(identifier: NSCalendarIdentifierGregorian)
      return calendar?.dateFromComponents(components)
  }
  
  class func dateFromString(string: String) -&gt; NSDate?  {
      let dateFormatter = NSDateFormatter()
      dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss-SSS"
  
      if let stringDate = dateFormatter.dateFromString(string) {
          return stringDate
      } else {
          return nil
      }
  }
  
  func ISOStringFromDate() -&gt; String {
      let dateFormatter = NSDateFormatter()
      dateFormatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
      dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSS"
  
      return dateFormatter.stringFromDate(self).stringByAppendingString("Z")
  }
  
  class func dateFromISOString(string: String) -&gt; NSDate? {
      let dateFormatter = NSDateFormatter()
      dateFormatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
      dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
  
      if let stringDate = dateFormatter.dateFromString(string) {
          return stringDate
      } else {
          return nil
      }
  }
  </code></pre>
  
  <p>Any help with how I can make NSDate() be my local timezone so this one day behind issue can go away? Any help is greatly appreciated :) </p>