possible lock order issue with epicsTimerQueueRelease()

The helgrind tool finds a possible lock order issue in epicsTimerQueueAllocate()/epicsTimerQueueRelease() as used in callback.c.

I'm mostly convinced that this is a false positive and no deadlock is possible. However, the timer queue code is confusing to me, so I might be wrong. Also, the potential conflict can be avoiding by removing what looks like a pointless cycling through a mutex.

> timerQueueActiveMgr::~timerQueueActiveMgr ()
> {
> epicsGuard < epicsMutex > locker ( this->mutex );
> }

May be related to one of the issues reported in lp:1479316