title: Cancel request for Alamofire image
body: <p><strong>Basic Information:</strong>
  I have a tableView and each tableView cell <strong>containing an image and few labels</strong>.
  I use tableView <strong>prefetch data</strong> method to make API calls to fetch data as the tableView scrolls.</p>
  
  <p><strong>Issue:</strong>
  Sometimes I see <strong>a particular cell showing an image of some other cell</strong>. 
  This happens when I scroll a little faster than normal speed.
  Note: In order to overcome from this issue I just need to scroll the tableView up/down</p>
  
  <p><strong>Things tried:</strong>
  I have set the imageView to nil in <strong>prepare for reuse</strong> method.</p>
  
  <p><strong>The conclusion I have reached:</strong>
  By debugging the issue I understood that once a cell is visible I make an image request using Alamofire Image but I scroll it before we received the response. 
  So, what might be happening is that on receiving a response it is setting an image for the cell but that cell is not visible as I am reusing the cells. The cell contains some other data.</p>
  
  <p>Please let me know how can I cancel the request if the cell is not visible.
  Let me know if I am missing something in the question.</p>