We currently disable cursor blinking in the FBDevScreen constructor and re-enable it if necessary in FBDevScreen.shutdown().

We should do the same with fb0 screen blanking. We should read the value in /sys/class/graphics/fb0/blank in the FBDevScreen constructor, then write 0 to that file. On shutdown we should restore the old value.

If we fail to read or write the initial value we should issue a brief warning and continue.