title: ReactiveCocoa- How to dispose of a signal using 'switchToLatest'?
body: <p>I have a UITableViewCell with a viewModel property. As the tableview cell is getting reused I would like it to bind to properties of its <em>latest</em> viewModel, like so:</p>
  
  <pre><code>RAC(self.titleLabel, text) =
  [[RACObserve(self, viewModel) map:^id(MyViewModel *viewModel) {
      return RACObserve(viewModel, title);
  }]
  switchToLatest];
  </code></pre>
  
  <p>The problem I'm seeing is that the cell is never getting released when it should be. 
  Is there a way to dispose of the signal when the cell should be dealloc-ed?</p>