Fix issue 1274 - file security on multi-site installations
Merge pull request #1277 from jrfnl/Issue-1274-files-vs-multisite

Fix issue #1274 - file security on multi-site installations, props @jrfnl
Merge branch 'master' of git://github.com/Yoast/wordpress-seo into Issue-1242-metabox-loading