MediaWiki Math Extension Out of Sync

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http://serverfault.com – I am trying to run MediaWiki 1.19.2 on Ubuntu Linux (3.0.0-26-generic #42-Ubuntu AMD 64). It installs fine via tar.gz, however, I run into problems when trying to install the Math extension (via git clone https://gerrit.wikimedia.org/r/p/mediawiki/extensions/Math.git). I get the following error in the Apache logs: PHP Fatal error: Call to undefined method FSFileBackend::getRootStoragePath() in /var/www/abc.com/html/mediawiki-1.19.2/extensions/Math/Math.body.php on line 361, referer: http://intra.abc.com/wiki/index.php?title=Quality&action=submit so apparently, the latest Math extensio (HowTos)