restore the include file

there is a subtility I'm missing with argt testsuite
if not included, then flags define in the script
cgal_test_with_cmake are not passed to CXX_FLAGS

Arrangement_on_surface_2/test/Arrangement_on_surface_2/CMakeLists.txt

@@ -8,6 +8,7 @@ enable_testing()
 
 find_package(CGAL REQUIRED COMPONENTS Core)
 
+include (${CGAL_USE_FILE})
 # Since CMake-2.8.12: New CMake script, that defines the targets and
 # the CTest test cases.
 include(${CMAKE_CURRENT_SOURCE_DIR}/cgal_test.cmake)