Support gcc 5.2 detection for boost

Author: pieterlexis

m4/boost.m4

@@ -1295,6 +1295,8 @@ if test x$boost_cv_inc_path != xno; then
   # I'm not sure about my test for `il' (be careful: Intel's ICC pre-defines
   # the same defines as GCC's).
   for i in \
+    _BOOST_mingw_test(5, 2) \
+    _BOOST_gcc_test(5, 2) \
     _BOOST_mingw_test(5, 1) \
     _BOOST_gcc_test(5, 1) \
     _BOOST_mingw_test(5, 0) \