Ssh connection caching is now enabled automatically by git-annex. Only one
ssh connection is made to each host per git-annex run, which can speed some
things up a lot, as well as avoiding repeated password prompts. Concurrent
git-annex processes also share ssh connections. Cached ssh connections are
shut down when git-annex exits.
Note: The rsync special remote does not yet participate in the ssh
connection caching.
