*sh: steal Lann's fancy tmux ssh-agent trick

Let's try this for a few days. If it works and doesn't run into any edge
cases, we can get rid of `ssh-reagent` and perhaps even the `timeout3`
script.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Git: remove `ssh-add -l` from `git refresh` alias

With the more robust SSH auth socket handling in place, we likely don't
need this any more.

Signed-off-by: Wincent Colaiuta <win@wincent.com>