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 https://github.com/boostorg/thread/issues/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.
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