Disable unreachable code warning for MSVC

Author: igaztanaga

include/boost/container/detail/config_begin.hpp

@@ -41,6 +41,7 @@
    #pragma warning (disable : 4671) //  the copy constructor is inaccessible
    #pragma warning (disable : 4673) //  throwing '' the following types will not be considered at the catch site
    #pragma warning (disable : 4675) // "method" should be declared "static" and have exactly one parameter
+   #pragma warning (disable : 4702) // unreachable code
    #pragma warning (disable : 4706) // assignment within conditional expression
    #pragma warning (disable : 4710) // function not inlined
    #pragma warning (disable : 4714) // "function": marked as __forceinline not inlined