pthread functions are called without checking return values for error

[Richard <legalize@…>]

This is similar to ​https://svn.boost.org/trac/boost/ticket/2681

The errors are detected by coverity static analysis.

58    void lock()
59    {

CID 11713: Unchecked return value
60        pthread_mutex_lock(&m_);
61    }

68    void unlock()
69    {
  
CID 11714 (#1 of 1): Unchecked return value (CHECKED_RETURN)
1. check_return: Calling function "pthread_mutex_unlock(pthread_mutex_t *)" without checking return value (as is done elsewhere 6 out of 7 times). 
2. unchecked_value: No check of the return value of "pthread_mutex_unlock(&this->m_)". 
70        pthread_mutex_unlock(&m_);
71    }

[viboes]

Do you want the same outcome than #2681?

[Richard <legalize@…>]

I think using BOOST_VERIFY as was done in the other changeset is entirely reasonable.