[Seaside] Bug in Set backtracking

[David Shaffer]

...following up before I publish a patch to the 2.5 and 2.6a repo's... 
I suspect that many objects don't properly snapshot.  The only overrides
of the snapshotting messages in my 2.5-based image are mine.  What's
your position on how much the base Seaside should try to deal with
this?  Is my fix the preferred approach (fix it with a deeper copy)?  I
use this in several of my mutable model classes and it seems to
work...although I have been living with the "double backtracking" bug
and didn't know it :-/  Registering an object for backtracking clearly
requires an understanding of the backtracking mechanism.

David