Bug#1031076: Doesn't go to DPMS sleep anymore and settings always disabled

[Tormod Volden]

This line changes p2->dpms_enabled_p to zero when the Advanced windows
is opened the first time:

CHECKBOX (p2->dpms_enabled_p,  dpms_button);

(line 1324 in driver/demo-Gtk.c, in flush_dialog_changes_and_save)