Melchior FRANZ:

Melchior FRANZ:

- don't unlock an already unlocked mutex (Someone wanted to be on
  the safe side with this, but the result is undefined and makes
  pthread_mutex_destroy fail. Reference: manpage for
  pthread_mutexattr_gettype/The Open Group[1]: "Attempting to
  unlock a mutex of this type which is not locked results in
  undefined behaviour.")

- re-enabled all subsystem destructors again (this has been disabled
  because fgfs hung on exit, due to the mutex destroy failure from
  above.)

Reference:
  http://www.opengroup.org/onlinepubs/007908799/xsh/pthread_mutexattr_gettype.html