allow 'Allow machine to sleep' to work if 'Allow screen saver to star…

[rdp]

…t' is not checked

OK something weird is going on, where if "Allow screen saver to start" is checked then "Allow machine to sleep" checkbox has no effect.

But the weirder part is that rfbDisableScreenSaver seems to actually "have no effect" at all, by itself. It's very odd. With this commit the "Allow machine to sleep" checkbox always does something, at least...

[stweil]

@rdp, is this pull request still required or was #20 sufficient?

[rdp]

It's still useful. For config stuff :)