Ah, I think I found it:
http://www.mediawiki.org/wiki/Extension:WikimediaShopLink
On 2/25/14, Carcharoth carcharothwp@googlemail.com wrote:
Is anyone able to track down the history of the sidebar?
I noticed 'Wikimedia Shop' appeared there (recently?), and I can only find:
https://en.wikipedia.org/wiki/MediaWiki:Sidebar
How do I get from that to the actual pages where changes are being made?
Carcharoth