Completed rename support

[Matt Mackall]

The last piece of planned rename support, detection of directory
renames at merge time, is now in tip. When either side of a merge
moves all the files in a directory to another directory, files added
to that directory on the other branch of the merge will also be moved.

I'm planning to release 0.9.2 next Friday so testing here is
appreciated.

-- 
Mathematics is the supreme nostalgia of our time.