Hi,

I store lots of books under annex and every once in a while one of them gets updated and I don't really want to keep the old version. I know about the `unused` subcommand but it makes a bit difficult to identify what I would be dropping. I mean, at the point in time when I'm replacing a file I already know I don't want to keep in the annex, maybe there is a method that directly referrs to that file instead of globally garbage collecting obscurely named files. Now, this is what comes to my mind:

Alternative a

1. git-annex drop f
2. git rm f
3. mv new-f f
4. git-annex add f

Alternative b

1. git-annex unlock f
2. mv new-f f
3. git-annex add f
4. git commit -am blah
5. git checkout HEAD^
6. git-annex drop f
7. git checkout master

As you can see neither option is that pretty. Is there any way to say 'drop f in revision r' or something similar?

Thank you!
