bug#2152: 23.0.90; NS: Hang with proxy icon drag for removed file

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

Steps to reproduce:
  1. $ touch ~/foo
  2. $ Emacs.app/Contents/MacOS/Emacs -Q
  3. C-x C-f ~/foo RET
  4. $ rm ~/foo
  5. Start dragging the proxy icon in the Emacs title bar.

Result:
  Emacs no longer responds to keyboard or mouse events.

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp

In GNU Emacs 23.0.90.1 (powerpc-apple-darwin9.6.0, NS apple-appkit-949.43)
 of 2009-02-02 on yamamoto-mitsuharu-no-power-mac-g5.local
Windowing system distributor `Apple', version 10.3.949
configured using `configure  '--with-ns''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: ja_JP.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<menu-bar> <help-menu> <send-emacs-bug-report>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.