CPTableView: When columns or rows dragging ends, enqueue the dragged views so they can be available when you drag again the column if they haven't been unloaded before.

The 2nd time you drag the same column/row, reduces -dragViewFor... duration by 90% according to webkit profiling.

AppKit/CPTableHeaderView.j

@@ -486,6 +486,8 @@ var _CPTableColumnHeaderViewStringValueKey = @"_CPTableColumnHeaderViewStringVal
     [self stopTrackingTableColumn:_activeColumn at:aLocation];
 
     [self setNeedsDisplay:YES];
+    
+    [_tableView _enqueueDraggingViews];
 }
 
 - (BOOL)shouldResizeTableColumn:(int)aColumnIndex at:(CGPoint)aPoint