Thoughts on file ids

[Martin Pool]

I don't think tying these things together is really an essential
aspect of Bazaar; as much as any attachment to file ids, Bazaar cares
about the idea that the implementation of these classes is abstracted
and we should be able to deal with implementations that don't actually
use file ids there.  There is no architectural reason why these keys
need to be the same.  Of course you are right that the change would
need to be made very carefully for both correctness and performance.

> Secondly, this would open the door to bugs like 'rename showing up as a delete and add'.

Right, we don't want to go backwards on that.  On the other hand,
there are other bugs about for instance multiply added files that may
be easier to tackle in this factoring.

As I think of them, path tokens really address Jelmer's #3 and being
clearer about these distinctions may allow using them.

Martin