Worked today on two action items from my last blog post:

* on-disk transfers in progress information files (read/write/enumerate)
* locking for the files, so redundant transfer races can be detected,
  and failed transfers noticed

That's all done, and used by the `get`, `copy`, and `move` subcommands.

Also, I made `git-annex status` use that information to display any
file transfers that are currently in progress:

	joey@gnu:~/lib/sound/misc>git annex status
	[...]
	transfers in progress: 
		downloading Vic-303.mp3 from leech

(Webapp, here we come!)

However... Files being sent or received by `git-annex-shell` don't yet
have this transfer info recorded. The problem is that to do so,
`git-annex-shell` will need to be run with a `--remote=` parameter. But
old versions will of course fail when run with such an unknown parameter.

This is a problem I last faced in December 2011 when adding the `--uuid=`
parameter. That time I punted and required the remote `git-annex-shell` be
updated to a new enough version to accept it. But as git-annex gets more widely
used and packaged, that's becoming less an option. I need to find a real
solution to this problem.
