gdm and xdm just stopped working

["Thomas E. Vaughan" <vaughan@tensor.nssl.noaa.gov>]

After running dselect this morning, I noticed that gdm would fail to start
the X server.  So I installed xdm instead, and it has the same problem.
xinit and startx still work.

----------begin /var/log/xdm.log----------
X: user not authorized to run the X server, aborting.
xdm error (pid 756): server unexpectedly died
xdm error (pid 756): Server for display :0 can't be started, session disabled
---------- end  /var/log/xdm.log----------

-- 
Thomas E. Vaughan <thomas.vaughan@nssl.noaa.gov>
CIMMS/NSSL, Norman, OK, USA