New versions of boost and cmake need to be told to look in boost's library…

New versions of boost and cmake need to be told to look in boost's library folder to find boost's libraries
when building on windows.  Bizarre.

dlib/cmake_utils/add_python_module

@@ -52,6 +52,8 @@ set(Boost_NO_BOOST_CMAKE ON)
 if (NOT WIN32)
     set(BOOST_LIBRARYDIR ${BOOST_LIBRARYDIR} $ENV{BOOST_LIBRARYDIR}  
             /usr/lib/x86_64-linux-gnu/)
+else()
+    link_directories($ENV{BOOST_LIBRARYDIR})
 endif()
 if (PYTHON3)
     # On some systems the boost python3 module is called python-py34 so check