Fix to 2013-09 LWG Motion 7:

[comparisons] Fix incorrect application of N3789 to the working paper:
  - Add 'constexpr' to
      std::equal_to<>::operator()
      std::not_equal_to<>::operator()
      std::greater<>::operator()
      std::less<>::operator()
      std::greater_equal<>::operator()
      std::less_equal<>::operator()
  - Reorder 'bool constexpr' to 'constexpr bool' in
      std::logical_or<T>::operator()
      std::logical_and<T>::operator()
      std::logical_not<T>::operator()

Also fixes 14882:2014 DIS JP 08, fixes 14882:2014 DIS JP 09, fixes #291.