Fixed timeout conditions in named semaphores

- Adding no-timeout case
- Fixed timeout conditions:
  The nowtime was not updated in retrying loop.
  If rc!=0, named semaphores always retried sem_trywait().
Fixed destructor in named semaphores

- sem_destroy() is not implemented in OS X.
- Unnamed semaphores should use sem_close() instead of sem_destroy().
Merge pull request #29 from yuya-oc/osx-semaphore-fix

Fixed named semaphore in OS X