[xmonad] focus but hidden

[Michael F. Lamb]

> I wonder what more we could do to signal something has floated.

Another $.02...

I'd like windows to float whenever I use mod+drag to resize
or move them around---as they do now---but I never use
alt+click to float a window in-place without changing its
position/dimensions. When I alt+click a window it is almost
always a mistake.

Since it's obvious that a window has been floated when I
"pull it out" of the tiled formation by dragging, it would
be sufficient and intuitive for me if alt+click were
ignored unless I begin dragging.

I have no idea how complex this idea becomes in code.