[rfc] bzr-colo into core

[Gordon Tyler]

It seems to me that a potential solution would be to make the repository
aware of branches, i.e. the repository would hold the list of pointers of
branch names to revisions (since that's all a branch is, right?).

With this in place, you could do the colocated thing where the working
tree has the repo embedded inside .bzr and be able to switch the working
tree between branches. Or you could do the shared repo in the parent dir
thing and have multiple working trees pointing to different branches in the
shared repo. In both cases, the working tree is essentially a light-weight
checkout with an additional pointer to the particular branch inside the
repo.

I suspect though that this is not backwards compatible since it would mean
both a repo and working tree format change. However, since this is planned
for bzr 3.0, I don't think that kind of change should be considered
unacceptable. Sometimes backwards compatibility has to be broken to make
progress.

Ciao,
Gordon