title: Custom UITableViewCells repeating when navigating to viewcontroller
body: <p>I am making a running app, and would like the user to see the races/marathons in their city. When clicking on the cell the user is navigated to a new view controller with details of the marathon. But upon pressing the back button to go back to the table the cells repeat. for example, if scrolling on the table it will display cell 1, cell 2,cell 3, cell 4,cell 1, cell 2,cell 3, cell 4 and will repeat more every time I navigate to the view controller with the table. 
  The code for the table is:</p>
  
  <pre><code>//MARK: TableView
  func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -&gt; Int {
      return exhibitions.count
  }
  func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -&gt; UITableViewCell {
      let singleCell: marathonTableViewCell = tableView.dequeueReusableCellWithIdentifier("marathonCell") as! marathonTableViewCell
  
  
      singleCell.marathonName.text = exhibitions[indexPath.row]
      singleCell.entryNumber.text = "\(entryNumber[indexPath.row])"
      singleCell.entries.text = "\(entires[indexPath.row])"
  
  
  
  
      return singleCell
  
  
  }
  
  
  
  func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
  
  
  
      self.performSegueWithIdentifier("marathonDetail", sender: self)
  
  
  }
  
  override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
      if(segue.identifier == "marathonCardDetail"){
  
          var upcoming: marathonDetailViewController = segue.destinationViewController as! marathonDetailViewController
  
          let indexPath = self.marathonsTableView.indexPathForSelectedRow!
  
  
  
          let currentCell = marathonsTableView.cellForRowAtIndexPath(indexPath) as! marathonTableViewCell
  
          let marathonEvents = currentCell.marathonName.text
  
  
          upcoming.nameMarathon = marathonEvents
  
          self.marathonsTableView.deselectRowAtIndexPath(indexPath, animated: true)
  
  
  
  
      }
  }
  </code></pre>
  
  <p>I am using swift, Xcode 7, and Parse as my backend.</p>