$wgGrantPermissions are new in mediawiki, as part of moving grants being moved from OAuth to core
https://gerrit.wikimedia.org/r/#/c/259062/
these are now needed to be able to edit wikidata (soon as wmf11 is re-deployed) with the new bot passwords feature. (if not more things)
https://lists.wikimedia.org/pipermail/wikitech-l/2016-January/084501.html