Provide a way to access the last modified revision from the Tree API

[Jelmer Vernooij]

  affects bzr

The most common reason that existing code looks directly at inventory
objects is that it has to find out the last modified revision, something
that is not possible using the Tree API.

It would be nice if we could have such a call and make .inventory
optional, that would make it possible for bzr-{svn,git,hg} to avoid a
lot of code trying to come up with inventory entry objects on the fly.

[John A Meinel (jameinel)]

I agree that this is the most common. I doubt that bzr-svn et al could get rid of .inventory entirely, but certainly it could be rare for them to need to populate it.

I think there is an ugly hack in doing:
  tree.iter_entries_by_dir(file_id).next()[1].revision

But I'm not positive about that.

[John A Meinel (jameinel)]

I should mention, it at least raises the question of whether last-modified is what we want, or whether we want an InventoryEntry.