revset: fix parameter name in implementation of follow()
$ hg init t $ cd t $ echo a > a $ hg add a $ hg commit -m test $ rm .hg/requires $ hg tip abort: index 00changelog.i unknown format 2! [255] $ echo indoor-pool > .hg/requires $ hg tip abort: unknown repository format: requires feature 'indoor-pool' (upgrade Mercurial)! [255]