Windows, because xrange uses 32bit integers and __getslice__ gets 64bit integers

LP #642728: Fixed TypeError on nested multi part messages in MailHost. Thanks to Mail Derstappen for the patch!

- added forward-compatibility shim for UserFolder (this makes it easier to write CMF migration code)

make sure that the browser:view directive doesn't clobber security declarations for attributes which are not included in allowed_attributes or allowed_interface but which already have security declarations in a base class's security info. This is needed to provide access to, e.g., restrictedTraverse on views that subclass Traversable