[rfc] bzr-colo into core

[jbowtie at amathaine.com]

So, from the documentation side, there are three audiences to consider:

1) New Bazaar users; the colo workflow should be clearly and carefully
documented to avoid confusing them. In particular, we want to make
sure stuff relevant to non-colo workflows is clearly marked as
alternative.

2) Existing Bazaar users who want to switch - we need to be clear
about how this affects existing users of foreign repositories,
lightweight checkouts, stacked branches, multiple heavyweight
branches, and any changes in behaviour of existing commands.

3) Existing Bazaar users who want to keep using a non-colo workflow -
need to be clear about any user-facing changes that affect those
workflows, as well as a good guide to which workflows are most
appropriate to specific tasks. They also need to be able to find
relevant documentation clearly marked within the primary
documentation.