NativeWindow/OSX: Fix RunOnThread/RunLater - Properly determine 'forkOnMain' via onMain && ( isOnMain || 0 < delay )
NEWT/Fullscreen (Bug 836): Exit re-parenting fullscreen w/ [invisible-exit-visible] (-> like reparent); Always force focus; X11: Always use ALWAYSONTOP.

- Remove unused 'fullscreenUseSpanningMode' state

- Exit re-parenting fullscreen w/ [invisible-exit-visible] (-> like reparent)
  solves X11 issue, where the NEWT window doesn't 'return to it's parent'.
  Probably also fixes Bug 836!

- Always force focus when enter and exit FS

- X11: Always use ALWAYSONTOP
  No reason to behave different (spanning and normal-fs)
NEWT/OSX (Bug 836): Lifecycle operations performed on main-thread must be synchronized (wait-until-done)

Wait-until-done (main thread):
  - WindowDriver.close0(..)
  - WindowDriver.initWindow0(..)

Otherwise a re-queued operation (i.e. CALayer attachment)
will mixup the order ..

Experienced w/ fullscreen exit.