Work around performance decrease introduced in Zope 2.12.23.

Otherwise, we use superclass' __contains__ implementation, which uses
objectIds, which is inefficient in HBTreeFolder2 to lookup a single key.

This commit reverts fdf4fa44 that does not work in reality.

product/ERP5Type/Core/Folder.py

@@ -1054,6 +1054,8 @@ class Folder(CopyContainer, CMFBTreeFolder, CMFHBTreeFolder, Base, FolderMixIn):
         return False
       return CMFBTreeFolder.hasObject(self, id)
 
+  __contains__ = hasObject
+
   # Override Zope default by folder id generation
   def _get_id(self, id):
     if self._getOb(id, None) is None :