bug#13979: 24.3.50; NS: scroll-bar not draggable

[Darren Hoo]

turn on scroll-bar mode
 (scroll-bar-mode t)

then open a file and drag the scroll bar, it shows:

`mouse-on-link-p: Wrong type argument: listp, handle'

the stacktrace:

Debugger entered--Lisp error: (wrong-type-argument listp handle)
  mouse-posn-property((#<window 0x10506e250 on *info*>
vertical-scroll-bar (4 . 428) 95079520 handle) follow-link)
  mouse-on-link-p((#<window 0x10506e250 on *info*> vertical-scroll-bar
(4 . 428) 95079520 handle))
  mouse--down-1-maybe-follows-link(nil)

Also with scroll-bar turned on, horizontally splitted windows can not be
resized by dragging.

In GNU Emacs 24.3.50.3 (x86_64-apple-darwin12.2.1, NS apple-appkit-1187.37)
 of 2013-03-17 on Darren-rMBP
Bzr revision: 112060 jan.h.d@swipnet.se-20130316142237-fbp077v13rwbq20y
Windowing system distributor `Apple', version 10.3.1187
Configured using:
 `configure --with-ns'