Set this because CMake search for python is wacked on ubuntu and won't look for…

Set this because CMake search for python is wacked on ubuntu and won't look for new python otherwise.

dlib/cmake_utils/add_python_module

@@ -68,6 +68,7 @@ if (PYTHON3)
     if (NOT Boost_FOUND)
         FIND_PACKAGE(Boost 1.41.0 COMPONENTS python)
     endif()
+    set(Python_ADDITIONAL_VERSIONS 3.5)
     FIND_PACKAGE(PythonLibs 3.4 REQUIRED)
 else()
     FIND_PACKAGE(Boost 1.41.0 COMPONENTS python)