ENH: fix for bug 1304

Modules/UseSWIG.cmake

@@ -168,8 +168,9 @@ MACRO(SWIG_ADD_MODULE name language)
     SWIG_ADD_SOURCE_TO_MODULE(${name} swig_generated_source ${it})
     SET(swig_generated_sources ${swig_generated_sources} "${swig_generated_source}")
   ENDFOREACH(it)
+  GET_DIRECTORY_PROPERTY(swig_extra_clean_files ADDITIONAL_MAKE_CLEAN_FILES)
   SET_DIRECTORY_PROPERTIES(PROPERTIES
-    ADDITIONAL_MAKE_CLEAN_FILES "${ADDITIONAL_MAKE_CLEAN_FILES};${swig_generated_sources}")
+    ADDITIONAL_MAKE_CLEAN_FILES "${swig_extra_clean_files};${swig_generated_sources}")
   ADD_LIBRARY(${SWIG_MODULE_${name}_REAL_NAME}
     MODULE
     ${swig_generated_sources}