Not a lot of progress on import tree today I feel..

Started off by adding a QuickCheck test of the content identifier log, which did find one bug in that code.

Then started roughing out the core of the importing operation, which involves building up git trees for the files that are imported. But that needs a way to graft an imported tree into a subdirectory of another tree, and the only way I had available to do it needed to read in the entire recursive tree of the current branch, which would be slower and use more memory than I like.

So, got sidetracked building a git tree grafter. It turns out that the export tree code also needs to graft a tree (into the git-annex branch), and did so using the same innefficient method that I want to avoid, so it will also be able to be improved using the grafter.

Unfortunately, I had to stop for the day with the grafter not quite working properly.