Extensions are of four types:
* Core: they come with Mediawiki core and are updated with it
* Contrib, available through ExtensionDistributor [1]: updated manually when Mediawiki is updated
* Contrib, not available through ExtensionDistributor: not updated, stored in SVN for convenience
* Custom: GoogleCoop and OOoIDLtags, stored in SVN

[1] https://www.mediawiki.org/wiki/Special:ExtensionDistributor