outside edges of frame, not inside edges.
(windmove-coordinates-of-position): Convert into wrapper to new
function `windmove-coordinates-of-window-position';
`compute-motion' always applies to selected window.
(windmove-coordinates-of-position): Update documentation to refer
to Emacs 21 Lisp Reference Manual.
(windmove-find-other-window): Fix off-by-one errors for max x,y.
