Merge branch 'master' into develop
Added shared_array constructor from nullptr, per #8894.
Check return values of pthread_* calls with BOOST_VERIFY, per #8904.
Check return values of pthread_* calls with BOOST_VERIFY, per #8898
Add support for BOOST_SP_USE_STD_ATOMIC
Update atomic_count.hpp to match sp_counted_base.hpp.
Remove obsolete _nmt headers.
Add intrusive_ptr<>::detach()

This provides a way to escape from automatic reference counting, and taking
manual control of the reference.  Useful when interfacing to a C API that
expects a pointer with an elevated reference count.

Similar to std::unique_ptr<>::release().
Add one more intrusive_ptr test case.
Add add_ref parameter to intrusive_ptr::reset, add tests for reset.
Deboldify, clean up intrusive_ptr.html.
Update make_shared for arrays to conform to N3870

Update make_shared and allocate_shared for arrays to be confined to the
set of overloads specified in N3870.
Update make_shared for arrays documentation
Minor cosmetic changes in make_shared for arrays
Add make_unique for arrays and objects
Update make shared for arrays documentation
Add top-level make_unique.hpp and documentation
Minor documentation corrections
Add fourth form of make_unique for objects

To support initialization syntax that Args&&... cannot forward perfectly.
make_unique tests run only for C++11 compilers