Wrote nice pure transition calculator, and ugly code to stage its results
into the git-annex branch. Also had to split up several Log modules
that Annex.Branch needed to use, but that themselves used Annex.Branch.
The transition calculator is limited to looking at and changing one file at
a time. While this made the implementation relatively easy, it precludes
transitions that do stuff like deleting old url log files for keys that are
being removed because they are no longer present anywhere.
Works, more or less. --dead is not implemented, and so far a new branch
is made, but keys no longer present anywhere are not scrubbed.
git annex sync fails to push the synced/git-annex branch after a forget,
because it's not a fast-forward of the existing synced branch. Could be
fixed by making git-annex sync use assistant-style sync branches.
