RFC: genbt5list may depend on non-standard Python modules.

Until now it wasn't but with python3, import on future (not part of Python
library) means ${buildout:executable} is not enough. Anyhow, genbt5list should
be executed with all eggs IMO to avoid such problem.

stack/erp5/buildout.cfg

@@ -317,7 +317,7 @@ recipe = plone.recipe.command
 stop-on-error = true
 genbt5list = ${erp5:location}/product/ERP5/bin/genbt5list
 command =
-  echo '${local-bt5-repository:list}' |xargs ${buildout:executable} ${:genbt5list}
+  echo '${local-bt5-repository:list}' |xargs ${eggs:bin-directory}/python ${:genbt5list}
 update-command = ${:command}
 
 [erp5_repository_list]