use a generic parts/ path

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@32458 20353a03-c40f-0410-a6d1-a30d3c3de9de

buildout/python-2.4/buildout.cfg

@@ -13,7 +13,7 @@ parts =
 recipe = hexagonit.recipe.cmmi
 url =
   http://python.org/ftp/python/${buildout:python_version_full}/Python-${buildout:python_version_full}.tgz
-prefix = ${buildout:directory}/parts/python${buildout:python_version}
+prefix = ${buildout:parts-directory}/python${buildout:python_version}
 configure-options =
   --enable-unicode=ucs4
   --with-threads