Patch adds a "from __future__" import that doesn't affect newer python's but
allows python 2.5.4 to run the code (tested under scratchbox, n900 build environment)

It turns out that using base + sizeof(struct) is not a good way to
access an array at the end of a struct. For SpicePalette sizeof is 16, but
offset of ents is 12. Using this calculation in the demarshaller breaks
things badly, so now we use the actual array member.

Remove all uses of @end in the marshaller, instead just using
the C struct array-at-end-of-struct. To make this work we also remove
all use of @end for switches (making them C unions).

We drop the zero member of the notify message so that we can avoid this
use of @end for a primitive in the marshaller (plus its useless to send
over the wire).

We change the offsets and stuff in the migration messages to real pointers.

This way we can check attributes on the member.