bug#16647: Imprecisions with window-resizing cursors

[E Sabof]

On current trunk version, from emacs -Q

1)

(progn
  (scroll-bar-mode -1)
  (split-window-right)
  )

Slowly move the mouse from left to right across the vertical line splitting the 
windows. Once the mouse goes past the black line, it's still shown as <=>, 
although clicking-and-dragging on that area won't have any effect.

2)

C-x 2

Move the cursor from top to bottom, across the mode-line. Once the cursor 
enters the mode-line, it won't change to a "resize" cursor, although it's 
already possible to drag.

3)

C-x 1
(set-window-margins nil (car (window-margins)) 10)
C-x 3

Move the cursor from right to left, across the divider. Once the mouse enters 
the right margin, it will still be displayed as <=>, although it's not possible 
to resize by clicking there.

Evgeni

GNU Emacs 24.3.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.6.4) of 
2014-02-05 on ubuntu