POSIX recursive mutex

[Marty Kraimer <mrk@aps.anl.gov>]

A problem using pthread_mutex to implement epicsMutex is that pthreads does not 
provide a pthread_mutex_lock with a timeout. Thus the only way I see to 
implement epicsMutexLockWithTimeout is to do something like
timeleft = timeout;
while(timeleft>0.0) {
    if(pthread_mutex_trylock(...)==success) break;
    epicsThreadSleep(shortTime);
    timeleft -= shortTime;
}

I am not bsure this is a good idea. What do you think?

Marty