Currently, function_requires is a wrapper around BOOST_CONCEPT_ASSERT
and is marked for deprecation by the docs [1]. This PR substitutes all
calls to function_requires with calls to BOOST_CONCEPT_ASSERT in both
code and tests.
Also remove #include <boost/concept_check.hpp> from all files
(including parallel_property_maps.hpp) and leave it only in
property_map.hpp
[1]: http://www.boost.org/doc/libs/1_61_0/libs/concept_check/reference.htm#deprecated-functions
