I did fresh (first install) with nanoboot and DSM 5.0-4494 and then update 1.
And button.ko was not present at all.
So I copied button.ko, made all right permisions (CHMOD), did all steps required to get button working, restarted.
If I list loaded modules now (LSMOD) - I get "button" listed, but "cat /proc/acpi/event" does not give any output when pressing power button.