bug#12258: 24.2.50; OS X dialog box locks emacs

[Ivan Andrus <darthandrus@gmail.com>]

Starting from emacs -Q, evaluating the following causes a dialog to
appear.  It is impossible to dismiss the dialog and impossible to
interact with the rest of emacs. 

(let ((last-nonmenu-event nil)
      (use-dialog-box t))
  (y-or-n-p "Cache preamble? "))

It should be noted that I found this when I clicked on the
preview-at-point toolbar button in AUCTeX, so artificially setting
last-nonmenu-event seems justifiable.

In GNU Emacs 24.2.50.4 (i386-apple-darwin10.8.0, NS apple-appkit-1038.36)
of 2012-08-22 on oroszlan.local
Bzr revision: 109750 lekktu@gmail.com-20120822113025-9kha71kjrnrtrx0j
Windowing system distributor `Apple', version 10.3.1038
Configured using:
`configure '--with-ns''

Important settings:
  value of $LC_CTYPE: UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: LaTeX

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

Recent input:
M-x r e p o <tab> r <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Applying style hooks... done
Loading vc-hg...done
Making completion list...
user-error: Beginning of history; no preceding item
user-error: End of history; no default available
user-error: Beginning of history; no preceding item
ns-copy-including-secondary: The mark is not set now, so there is no region

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils help-mode vc-hg preview prv-emacs byte-opt tex-bar
tex-buf toolbar-x noutline outline font-latex warnings bytecomp
byte-compile cconv macroexp latex easy-mmode edmacro kmacro tex-style
tex latexenc ac-slime-autoloads ace-jump-mode-autoloads
ack-and-a-half-autoloads adaptive-wrap-autoloads
applescript-mode-autoloads auctex-autoloads tex-site info easymenu
browse-kill-ring-autoloads buffer-move-autoloads c-eldoc-autoloads
columnify-autoloads command-frequency-autoloads company-autoloads
debbugs-autoloads diff-hl-autoloads drag-stuff-autoloads
durendal-autoloads ein-autoloads emstar-autoloads feature-mode-autoloads
goto-last-change-autoloads graphviz-dot-mode-autoloads
highlight-parentheses-autoloads highlight-symbol-autoloads
hl-sexp-autoloads jump-char-autoloads keyfreq-autoloads
linum-relative-autoloads mark-multiple-autoloads
markdown-mode+-autoloads markdown-mode-autoloads
multiple-cursors-autoloads paredit-autoloads parenface-autoloads
python-mode-autoloads redo+-autoloads rw-hunspell-autoloads
scpaste-autoloads htmlize-autoloads scss-mode-autoloads
slime-clj-autoloads slime-fuzzy-autoloads slime-ritz-autoloads
smarter-compile-autoloads smex-autoloads speck-autoloads
swank-clojure-autoloads advice help-fns advice-preload
clojure-mode-autoloads slime-repl-autoloads slime-autoloads
undo-tree-autoloads vala-mode-autoloads websocket-autoloads
wgrep-autoloads xml-rpc-autoloads package time-date tooltip ediff-hook
vc-hooks lisp-float-type mwheel ns-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment lisp-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer loaddefs
button faces cus-face files text-properties overlay sha1 md5 base64
format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process ns multi-tty emacs)