i've been using keychain for some time now, and for a while i was confused by the result of trying to start a fresh ssh-agent via `keychain --timeout 600.` i'd been expecting that ssh-agent itself would be passed the timeout via its "-t life" option, ensuring that any keys added to it have a default timeout. instead it looks like the timeout is only passed to the ssh-add invocations for keys to be immediately added.

i've attached a patch that works for my keychain usage. i left the ssh_timeout in the ssh-add invocations as this allows keychain to add a key with a timeout that overrides that of a running ssh-agent.

if this is not directly patched, perhaps the documentation could be changed from describing the timeout as "conveyed to ssh-agent" to "conveyed to ssh-add?" (i'd guess that was the source of my initial confusion)

thanks in advance!