User-Agent:       Mozilla/5.0 (X11; Linux x86_64; rv:46.0) Gecko/20100101
Firefox/46.0
Build Identifier: 

After upgrading to the latest OpenSSH, if you have a configuration
that enables X forwarding in general but your current session does
not have $DISPLAY set, ssh prints an error message about it on every
connection. Specifically, it reports:

    DISPLAY "(null)" invalid; disabling X11 forwarding

This behavior did not exist before the upgrade. This is a divergence from
historical behavior and screws up any number of things.

Reproducible: Always

Steps to Reproduce:
1.Have a host, call it THEHOST, and a key that will work for the host, call it
$HOME/.ssh/id_rsa.
2.Run:
   env - ssh -F /dev/null -o "ForwardX11 yes" -i $HOME/.ssh/id_rsa THEHOST
/bin/true

Actual Results:  
ssh complains:
   DISPLAY "(null)" invalid; disabling X11 forwarding

Expected Results:  
No complaint. Silence about $DISPLAY being unset, because this is routine.

OpenSSH version: openssh-6.6p1-11.1.x86_64

This report is a carbon copy of

https://bugzilla.redhat.com/show_bug.cgi?id=1303260