explicit include Products.CMFCore to avoid core permission error if loaded early with Plone 4

If you want to laod this early in your buildout you may get an error related to permission cmf.ModifyPortalContent. The line above fixes this. see: http://plone.org/documentation/manual/upgrade-guide/version/upgrading-plone-4.0-to-4.1/updating-add-on-products-for-plone-4.1