.bashrc directly call keychain without verify if there are any existing $SSH_AUTH_SOCKS exists in environment

[Zekta Chan]

I am not sure this is from keychain or the package warpper in ubuntu
"eval `keychain --eval id_rsa`" in .bashrc
which will overwrite existing agent forwarding socket variable...

e.g. in A->B->C setting, if keychain is installed in the middle server (B)
the agent forwarding will be break, since B connect the agent on itself instead of forwarding to A's agent.
the script should take ENV variable in a higher priority

A simple if should fix the problem
if test _$SSH_AUTH_SOCK != _ ; then
        echo "SSH Agent Detected"
else
        eval `keychain --eval id_rsa`
fi

Thanks