Recent keyboard changes breaks quitting

[Chong Yidong]

Hi Eli, somehow your latest changes to keyboard.c broke quitting:

M-x C-g
  => The cursor remains in the minibuffer.

A second C-g is needed to exit the minibuffer.
I verified that this behavior was introduced by

  revno: 110138
  fixes bugs: http://debbugs.gnu.org/12447 http://debbugs.gnu.org/12326
  committer: Eli Zaretskii <address@hidden>
  branch nick: trunk
  timestamp: Sat 2012-09-22 16:16:03 +0300
  message:
  Fix bugs #12447 and #12326 with infloop causes by idle timers, update docs.

  src/keyboard.c (timer_check_2): Move calculation of 'timers' and
  'idle_timers' from here ...
  (timer_check): ... to here.  Use Fcopy_sequence to copy the timer
  lists, to avoid infloops when the timer does something stupid,
  like reinvoke itself with the same or smaller time-out.

  lisp/emacs-lisp/timer.el (run-with-idle-timer)
  (timer-activate-when-idle): Warn against reinvoking an idle timer
  from within its own timer action.

  doc/lispref/os.texi (Idle Timers): Warn against reinvoking an idle timer
  from within its own timer action.