xsecurelock: saver_xscreensaver broken with xscreensaver version 6+

My xscreensaver was a glslideshow, and because the saver_xscreensaver script calls the glslideshow binary directly it now fail with xscreensaver version 6+.

XIO:  fatal IO error 2 (No such file or directory) on X server ":0"
      after 217 requests (217 known processed) with 0 events remaining.
X connection to :0 broken (explicit kill or server shutdown).

I’m guessing xscreensaver does some magic before calling glslideshow that xsecurelock doesn’t know about.