Goto mark when the it's already focused now selects previous (mru) window.
Quite common to just quickly check a marked window - more convenient to repeat
the binding instead of using super-tab.
Try to make it a bit more "action oriented":
An action exists independently of its binding. It could conceivable be invoked
by other means too.
Some weirdness from the marriage remain to weed out, but this is a working
stepping stone.
