This patch is not in the upstream pjproject and does unsafe things with
the timer->_timer_id and timer->_grp_lock values in pj_timer_entry_reset()
outside of the timer heap lock.  pj_timer_entry_reset() is also called for
timers that are not about to be rescheduled in a few places.

Change-Id: I4fe0b4bc648f7be5903cf4531b94fc87275713c1