[Twisted-Python] Transporting pb.Copyable classes?

[Jasper Phillips]

I've been passing around instances of pb.Copyable classes for some time,
registering them via pb.setCopierForClassTree()...  However, this doesn't
allow me to pass the classes themselves.

I dug around in jelly and found jelly.globalSecurity.allowInstancesOf(),
which seems to do what I want, but makes me nervious as it's pretty
buried...

Passing classes seems like a reasonable thing to do, but now I wonder if
there is some reason that jelly doesn't allow it (except via a buried method
call)?  Or is this just an accidental misfeature?

-Jasper