assistant unused file handling

Make sanity checker run git annex unused daily, and queue up transfers
of unused files to any remotes that will have them. The transfer retrying
code works for us here, so eg when a backup disk remote is plugged in,
any transfers to it are done. Once the unused files reach a remote,
they'll be removed locally as unwanted.

If the setup does not cause unused files to go to a remote, they'll pile
up, and the sanity checker detects this using some heuristics that are
pretty good -- 1000 unused files, or 10% of disk used by unused files,
or more disk wasted by unused files than is left free. Once it detects
this, it pops up an alert in the webapp, with a button to take action.

TODO: Webapp UI to configure this, and also the ability to launch an
immediate cleanup of all unused files.

This commit was sponsored by Simon Michael.

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/git-annex.mdwn b/doc/git-annex.mdwn
index 279fa24dd..3e239f7d6 100644
--- a/doc/git-annex.mdwn
+++ b/doc/git-annex.mdwn
@@ -1228,6 +1228,19 @@ Here are all the supported configuration settings.
   to close it. On Mac OSX, when not using direct mode this defaults to
   1 second, to work around a bad interaction with software there.
 
+* `annex.expireunused`
+
+  Controls what the assistant does about unused file contents
+  that are stored in the repository.
+  
+  The default is `false`, which causes
+  all old and unused file contents to be retained, unless the assistant
+  is able to move them to some other repository (such as a backup repository).
+
+  Can be set to a time specification, like "7d" or "1m", and then
+  file contents that have been known to be unused for a week or a
+  month will be deleted.
+
 * `annex.fscknudge`
 
   When set to false, prevents the webapp from reminding you when using