title: Memory issue in SDWebImage
body: <p>I am using SDWebImage in UICollectionView and UITableView. In both case, when the number of rows are high, from time to time the memory usage will go tremendous high and I receive a memory warning. </p>
  
  <p>Following is my profile image:</p>
  
  <p>You see, sometimes the memory usage goes to 182M.</p>
  
  <p>The main methods I used of SDWebImage are:</p>
  
  <pre><code>[[SDWebImagePrefetcher sharedImagePrefetcher] prefetchURLs:prefetchURLs];
  </code></pre>
  
  <p>and</p>
  
  <pre><code>[cell.dishImageView sd_setImageWithURL:[NSURL URLWithString:dish.imageURL]];
  </code></pre>
  
  <p>The later one is used in a UITableView.</p>
  
  <p>Has anyone run into the same problem?</p>
  
  <p>I'm using iOS 7 and iPhone 5.</p>