[MERGE] Rule-based preferences (EOL part 1 of 3)

[Stefan Monnier]

> So we have at least five categories of possible file, the first four
> of which we use at present:

>  0- internal files: inside .bzr; users should never touch it;
> rewritten by upgrades; propagated according to semantic rules; read
> and updated only by abstract apis and commands, not directly

Yes, example: .bzr/branch/tags
Note that this file is problematic, with unclear semantics, e.g. what to
do about conflicts.

I think that tags, ignore rules, and other rule, should be treated
fairly similarly.  Maybe also comment-amendments would fall into
that category.


        Stefan