Last modified: 2013-07-25 07:07:41 UTC
engines/LuaCommon/SiteLibrary.php contains a call to MWNamespace::getNamespaceContentModel, which was added in bf9bd497 (Gerrit change Ie012fd0ff) and did not make it into the 1.20 release. The call is present in the tree in 00d4b711ed, which http://www.mediawiki.org/wiki/Extension:Scribunto lists as being 1.20-compatible.
Related URL: https://gerrit.wikimedia.org/r/62409 (Gerrit Change Ib7f793c8559233aa1e7a128a03d133795cb06402)
Just delete the offending line, ContentHandler wasn't added until 1.21 so it's useless for 1.20.
https://gerrit.wikimedia.org/r/62409 (Gerrit Change Ib7f793c8559233aa1e7a128a03d133795cb06402) | change APPROVED and MERGED [by jenkins-bot]