[xmonad] darcs patch: add SshAgent module, to start ssh-agent when needed.

Hi all, I'm sending this rather than pushing, since we're close to a release. It's a new module to automatically start an ssh-agent, if one isn't running. I expect to find it useful. The reason for this is that the ordinary mechanism for starting a single ssh-agent for an X session doesn't seem to be working for me. And starting xmonad with `ssh-agent xmonad` does no good, because the ssh-agent exits as soon as I restart xmonad. David Sat Mar 29 11:49:11 CDT 2008 David Roundy * add SshAgent module, to start ssh-agent when needed.