* Re-fixed the EINTR bug that exists in some pthreads implementations.
It was originally fixed in https://svn.boost.org/trac10/ticket/6200 and
was accidentally disabled in 5b209c2.
* Made sure that the fix for the EINTR bug was consistently applied to
all code in the library.
* Made sure that all pthread_mutex_*() and pthread_cond_*() function
calls in the library were consistently decorated with
BOOST_THREAD_DISABLE_THREAD_SAFETY_ANALYSIS.