Minor pthrerad_mutex_unlock() issue

[Alexander Nedotsukov]

Guys,

During recent bug hunting in ports I found wired (or better to say as I 
think incorrect) behaviour of mutex unlocking code. Final unlock in code 
snippet given bellow will fail with EINVAL. There is special '?' switch 
in thr_mutex.c:mutex_lock_common() wich proceses mutexes with 0 
initialized m_owner field this way. Normally it should rerturn EPERM I 
guess. It was confusing to see EINVAL return from pthread_cond_wait() as 
a side effect of this. I was looking for some memory corruption instead 
of realizing that simply there is no prior mutex locking took place :-(

#include <stdio.h>
#include <pthread.h>
int main()
{
pthread_mutex_t m;
pthread_mutex_init(&m, NULL);
printf("%d", pthread_mutex_unlock(&m));
return 0;
}

I propose to remove special procesing for m_owner == NULL. Simple != 
curthread will be enough to report EPERM.

All the best,
Alexander.
ps.
Btw, pthread_cond_*() man pages need to be updated to indicate that 
there is EPERM return code possible.