[zsh] Attempt to make establishing an ssh-agent session more robust

I don't think this quite works though.

zprofile

@@ -3,8 +3,12 @@
 
 # Start SSH agent for password-less logins
 if [ -z "$SSH_AUTH_SOCK" -a -x "$SSHAGENT" ]; then
-    eval `ssh-agent -s`
-    trap "kill $SSH_AGENT_PID" 0
+    if ! pgrep -u $USER ssh-agent 1>/dev/null; then
+        eval $(ssh-agent -s > ~/.ssh_agent_vars)
+        trap "kill $SSH_AGENT_PID" 0
+    else
+        eval $(cat ~/.ssh_agent_vars)
+    fi
 fi
 
 autoload list_tmux_sessions