[CMake] add python subdir after searching for boost

CMakeLists.txt

@@ -30,8 +30,6 @@ IF(BUILD_PYTHON_INTERFACE)
 
   ADD_REQUIRED_DEPENDENCY("eigenpy")
   SET(BOOST_COMPONENTS ${BOOST_COMPONENTS} python)
-
-  ADD_SUBDIRECTORY(python)
 ENDIF(BUILD_PYTHON_INTERFACE)
 
 #find_package(Boost 1.58 REQUIRED unit_test_framework system serialization)
@@ -40,6 +38,10 @@ ENDIF(BUILD_PYTHON_INTERFACE)
 SEARCH_FOR_BOOST()
 INCLUDE_DIRECTORIES(SYSTEM ${Boost_INCLUDE_DIRS})
 
+IF(BUILD_PYTHON_INTERFACE)
+  ADD_SUBDIRECTORY(python)
+ENDIF(BUILD_PYTHON_INTERFACE)
+
 ADD_SUBDIRECTORY(include/curves)
 ADD_SUBDIRECTORY(tests)