Add env. variables to the X11 session by default

Need to add this file to ensure the environment variables are set at the X session level:

cat /etc/X11/Xsession.d/80appmenu-debug
export GTK_MENUPROXY="libappmenu.so"
export APPMENU_DISPLAY_BOTH=1

Note: /etc/profile.d does not work in this case (too late in the session setup process for the variables to be applicable to the gnome-panel launchers for example)