voutgl.m: hopefully, a stable Fullscreen mode for mozilla plugin, mouse double-click to toggle b/w windowed/fullscreen now works

Closes #809

and update comment - refs: #812

* backport [17405] don't bring the intf to the front when the last vout closes on OSX. It messes up the window focus.

* dvbsub: The spec assumes a 720x576 canvas. Set this as the original width/height, so the core can scale on non PAL video. refs #811

  - I get crashes when the MainThread does it's "FlushAllWindows".
    Quite possibly related to the fact that Carbon windows are not threadsafe..
  - I tried implementing similar behaviour in the mozilla plugin itself,
    but I cannot get it to even RENDER from there, so this will have to do for now.