Well, this took an hour on Christmas Day to track down!
The file /etc/X11/xinit/xinitrc.d/xinitrc needs to be in /etc/X11/xinit
instead!!!! BECAUSE /etc/X11/xdm/Xsession script runs all files in
/etc/X11/xinit/xinitrc.d directory BUT SO DOES xinitrc thus running
itself in a loop. Symptom is that logging in via xdm/kdm hangs.
It is not in /etc/X11/xinitrc.d as of xinitrc-3.3.