no display manager for 3 days

[Alan Simpson-Vlach <asimpson-vlach@laurelschool.org>]

Ever since a dist-upgrade that installed systemd and removed sysvinit-core, I have been unable to get a display manager.
I have tried slim, lightdm, and even installed gdm3.  Nothing works.

# /etc/init.d/slim/start

gives no error messages, but

# systemctl status slim.service

tells me that slim exited with status=1

The pertinent line appears to be

/usr/bin/X11/X: symbol lookup error: /usr/lib/xorg/modules/extensions/libglx.so: undefined symbol: LoadExtension

which is similar to what happens if I try xinit directly.

Trying lightdm I get 

lightdm.service start request repeated too quickly, refusing to start.

I think this is a systemd problem, but maybe it's a video driver problem?
I'm using the proprietary nvidia driver, which has been recompiled multiple times now.
Help, please.  I'd kinda like to have a working X11 again.

Thanks.