…ncludes.

1. Replace boost/bind.hpp includes with boost/bind/bind.hpp. This fixes
   deprecation warnings generated by the old header:

   The practice of declaring the Bind placeholders (_1, _2, ...) in the global
   namespace is deprecated.

2. Make inclusion of boost/bind/bind.hpp conditional in some cases, when the
   code actually conditionally uses boost::bind. Reduces compile-time overhead
   and fixes boostorg#307.

3. Remove some unnecessary uses of boost::ref. This allows to avoid including
   boost/core/ref.hpp in a few places, and avoids the associated template
   instantiation overhead in others.

4. Replace deprecated header includes with the more recent alternatives. For
   example: boost/detail/lightweight_test.hpp -> boost/core/lightweight_test.hpp,
   boost/ref.hpp -> boost/core/ref.hpp.

5. Replace some blanket includes with the more fine-grained ones. For example,
   boost/utility.hpp, boost/atomic.hpp. This reduces compile time overhead.

6. Add some missing includes, for example, boost/core/ref.hpp and
   boost/type_traits/is_same.hpp.

7. Replace uses of std::is_same with boost::is_same (with the corresponding
   included header) since the standard type_traits header presence and validity
   is not tested by the code. Using boost::is_same makes the code more portable.

1. Make inclusion of boost/bind/bind.hpp conditional in some cases, when the
   code actually conditionally uses boost::bind. Reduces compile-time overhead
   and fixes boostorg#307.

2. Remove some unnecessary uses of boost::ref. This allows to avoid including
   boost/core/ref.hpp in a few places, and avoids the associated template
   instantiation overhead in others.

3. Replace deprecated header includes with the more recent alternatives. For
   example: boost/detail/lightweight_test.hpp -> boost/core/lightweight_test.hpp,
   boost/ref.hpp -> boost/core/ref.hpp.

4. Replace some blanket includes with the more fine-grained ones. For example,
   boost/utility.hpp, boost/atomic.hpp. This reduces compile time overhead.

5. Add some missing includes, for example, boost/core/ref.hpp and
   boost/type_traits/is_same.hpp.

6. Replace uses of std::is_same with boost::is_same (with the corresponding
   included header) since the standard type_traits header presence and validity
   is not tested by the code. Using boost::is_same makes the code more portable.