Update for MSVC-14 CTP14.
Fix <type_traits> tests to check for the correct names!
Enable C++14 return type deduction for vc14.
Presence of pthread_yield is dependent on __USE_GNU.
Define BOOST_NO_CXX14_CONSTEXPR unless clang > 3.4.

Signed-off-by: Kohei Takahashi <flast@flast.jp>
Merge pull request #42 from Flast/bugfix/cxx14/clang34-constexpr

Define BOOST_NO_CXX14_CONSTEXPR unless clang > 3.4.
Rename BOOST_NO_CXX14_DIGIT_SEPARATOR to BOOST_NO_CXX14_DIGIT_SEPARATORS.
Fix name of BOOST_NO_CXX14_INITIALIZED_LAMBDA_CAPTURES in docs.
Merge branch 'develop' of https://github.com/boostorg/config into develop
Fix clang version checks.
Merge branch 'develop'