
The cursor() method is used by a window widget to set
the cursor while it is over that particular window.
Trying to use this method for another widget type,
such as a button, will result in program failure.

Apparently this method works only if it is called
after the target window is shown.

Considering the amount of coordinate checking needed to
keep track of which cursor to set where, and the fact that
most desktop environments and window managers already do
a sufficent job of dealing with cursors, I honestly can't
think of many situations where this feature would be worth
adding to an application. It is provided here as an example
anyway, just to show it's available.

The reset button (Alt+r) is there just in case the user
choses FL_CURSOR_NONE and can't find the cursor location.
