Fix simple issue with ASTableViewStressTest, make Table / Collection handle changes to dataSource / delegate.

AsyncDisplayKit/ASCollectionView.mm

@@ -234,7 +234,8 @@ - (void)reloadData
 
 - (void)setDataSource:(id<UICollectionViewDataSource>)dataSource
 {
-  ASDisplayNodeAssert(NO, @"ASCollectionView uses asyncDataSource, not UICollectionView's dataSource property.");
+  // UIKit can internally generate a call to this method upon changing the asyncDataSource; only assert for non-nil.
+  ASDisplayNodeAssert(dataSource == nil, @"ASCollectionView uses asyncDataSource, not UICollectionView's dataSource property.");
 }
 
 - (void)setDelegate:(id<UICollectionViewDelegate>)delegate

AsyncDisplayKit/ASTableView.mm

@@ -259,7 +259,8 @@ - (void)dealloc
 
 - (void)setDataSource:(id<UITableViewDataSource>)dataSource
 {
-  ASDisplayNodeAssert(NO, @"ASTableView uses asyncDataSource, not UITableView's dataSource property.");
+  // UIKit can internally generate a call to this method upon changing the asyncDataSource; only assert for non-nil.
+  ASDisplayNodeAssert(dataSource == nil, @"ASTableView uses asyncDataSource, not UITableView's dataSource property.");
 }
 
 - (void)setDelegate:(id<UITableViewDelegate>)delegate

examples/ASTableViewStressTest/Sample/ViewController.m

@@ -100,9 +100,6 @@ - (NSArray *)randomIndexPathsExisting:(BOOL)existing
 
 - (void)thrashTableView
 {
-  _tableView.asyncDelegate = self;
-  _tableView.asyncDataSource = self;
-
   [_tableView reloadData];
 
   NSArray *indexPathsAddedAndRemoved = nil;