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 5b209c2e834a89c93d308aa7ddb1dfd1207d929d.
Made sure that the fix for the EINTR bug was consistently applied to
all code in the library.
Made sure that all pthreadmutex() and pthreadcond() function
calls in the library were consistently decorated with
BOOST_THREAD_DISABLE_THREAD_SAFETY_ANALYSIS.