phabricator: do not read a same revision twice It's possible to set up non-linear dependencies in Phabricator like: o D4 |\ | o D3 | | o | D2 |/ o D1 The old `phabread` code will print D1 twice. This patch adds de-duplication to prevent that. Test Plan: Construct the above dependencies in a Phabricator test instance and make sure the old code prints D1 twice while the new code won't.