mouse wheeling beyond the end of the file

[Dan Jacobson]

Go to a file about two windows long and roll the mouse wheel,
supposing that you have it configured.

Notice how on the last page we can roll the text almost off the screen
upwards, exposing large amounts of 'outer space' beyond the end of the
file.

By default we should be stopped from wasting our "wheel breath" like
that.

Nobody lives there, mom said not to go loitering, end of file markers
present or not.