bundle2: track life cycle of parts...
bundle2: track life cycle of parts
We introduce a ``_generated`` attribute on parts. Coming changesets will
make it easier to update a part's contents after its creation. We need a way to track
if the part is still open to modification or if it is currently being generated
and should not be touched anymore.
As a bonus, we can now detect and crash if someone manages to write bogus code
to get a part generated twice.
