Update :pageinfo to use the new HTTP cache API.
Open the cache as readonly when retrieving a page size for :pageinfo.
iter.indexOf should return -1 when the elem is not found.
Bump minVersion to the latest ESR of 31.

Remove some version specific code that is no longer applicable.

--HG--
extra : amend_source : 803a60c3f5578a56a6832bd2dba9cce07784b873
Fix conflict between our tab styling and vertical tab addons.

Fixes issue #1196.
Fix more temporal dead zone fallout in contexts.bindMacro.

Fixes issue #1230.
Don't use `documentURI` for gu/gU.

--HG--
extra : rebase_source : 68b221e92b9234da8aebd6f0e19f89bd924956c1
Restore YouTube shortlink hack.

YouTube is broken again.
Ignore professed short URLs after AJAX tomfoolery.