Never start gpg agent with ssh-agent enabled on OSX. ssh-agent starts

automatically even if not running once an ssh session is started, and things
get confused if gpg-agent has ssh-support.

plugins/gpg-agent/gpg-agent.plugin.zsh

@@ -30,6 +30,8 @@ if ! gpg-connect-agent --quiet /bye > /dev/null 2> /dev/null; then
         if ssh-add -l > /dev/null 2> /dev/null; then
             # ssh-agent running, start gpg-agent without ssh support
             start_agent_nossh;
+        else if [][ "$OSTYPE" = "darwin"* ]; then
+            start_agent_nossh
         else
             # otherwise start gpg-agent with ssh support
             start_agent_withssh;