title: NSFetchResultsController section name based on nspredicate
body: <p>I have a predicate :</p>
  
  <pre><code>NSPredicate *predicate = [NSPredicate predicateWithFormat:
                                @"(nom BEGINSWITH[c] %@) OR (nom CONTAINS[c] %@)", _valeur, _valeur];
  </code></pre>
  
  <p>and a transient property to get result sorted by section :</p>
  
  <pre><code>_fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:_mainMOC sectionNameKeyPath:@"sectionIdentifier" cacheName:@"cache"];
  </code></pre>
  
  <p>I would like two sections ; first "begins with" and a second "contains". </p>
  
  <pre><code>- (NSString *)sectionIdentifier
  {
      return ([self.nom hasPrefix:@"predicateValue"]) ? @"Begins with" : @"Contains";
  }
  </code></pre>
  
  <p>How can i get the predicate value ?</p>
  
  <p>The only solution I found is using arrays from fetchRequest, but I'd rather use NSFetchedResultsController (best way in my opinion).</p>