Black screen (no backlight and image) in X after Kubuntu upgrade 13.04->13.10

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http://askubuntu.com – After upgrade from 13.04 to 13.10 I have troubles with Xorg - all boot process goes fine, but I'm can't see anything on screen (no backlight, and even if I use flashlight to try to backlight display manually it's still nothing on it) after Xorg start (KDE starts, and I can hear AC adapter (dis)connect sounds). Trouble is in Xorg only, framebuffer console (ctrl-alt-f2) works fine, backlight turns on when I switch to console and turns off again after I switch back to X. All worked fine before release upgrade. I'm running AMD64 version of Kubuntu 13.10 on Samsung RV508 (Intel i915 graphic, no (HowTos)