Make Skip Blank Windows work like Skip Identical Lines does: (dm)
   FWINLT/FWINRT are unchanged:
      If SBW is off then don't skip blank windows.
      If SBW is on then honour Skip Blank Windows Mode.
   FWINLTSKIP/FWINRTSKIP now work as follows:
      If SBW is off then honour Skip Blank Windows Mode.
      If SBW is on then don't skip blank windows.