title: TextField resignFirstresponder will crash in ios 7
body: <p>I am using <code>custom cell</code> with XIB. Now I scroll the table so the cell having the textFiled will be invisible. In this condition if i return the textField (means I call the <code>[textField resignFirstResponder]</code>) The app will crash and giving the error like  </p>
  
  <pre><code>[UITableViewCell _didChangeToFirstResponder:]: message sent to deallocated instance
  0xe05aa20. 
  </code></pre>
  
  <p>Please let me know if you have any idea about this.</p>