Support arc diff --edit under hg
Support arc diff --edit under hg

Summary: T1571

Test Plan: epriestley says it works

Reviewers: epriestley

Reviewed By: epriestley

CC: kwadwon, aran, Korvin

Differential Revision: https://secure.phabricator.com/D4883

coursera/arcanist,chundongwang/arcanist,fivestars/arcanist,kevinseelbach/arcanist,jra3/arcanist,codelabs-ch/arcanist,calblueprint/arcanist,Symplicity/arcanist,wharris/arcanist,phacility/arcanist,zhihu/arcanist,kevinseelbach/arcanist,phacility/arcanist,coursera/arcanist,folsom-labs/arcanist,Symplicity/arcanist,wxstars/arcanist,uber/arcanist,sneakpeeq/arcanist,r4nt/arcanist,codelabs-ch/arcanist,aik099/arcanist,r4nt/arcanist,coursera/arcanist,PageUpPeopleOrg/arcanist-patches,dguo-coursera/arcanist,julkiewicz/arcanist,wikimedia/phabricator-arcanist,zhihu/arcanist,phacility/arcanist,hach-que/arcanist,KieranHayes/arcanist,folsom-labs/arcanist,aik099/arcanist,PageUpPeopleOrg/arcanist-patches,uber/arcanist,hach-que/arcanist,uber/arcanist,uber/arcanist,chundongwang/arcanist,sneakpeeq/arcanist,Khan/arcanist,alexmv/arcanist,KieranHayes/arcanist,dguo-coursera/arcanist,memsql/arcanist,wharris/arcanist,dguo-coursera/arcanist,codelabs-ch/arcanist,aik099/arcanist,wharris/arcanist,PageUpPeopleOrg/arcanist-patches,zhihu/arcanist,Symplicity/arcanist,wxstars/arcanist,eSpark/arcanist,Symplicity/arcanist,r4nt/arcanist,folsom-labs/arcanist,julkiewicz/arcanist,Khan/arcanist,wxstars/arcanist,eSpark/arcanist,kevinseelbach/arcanist,wharris/arcanist,folsom-labs/arcanist,calblueprint/arcanist,memsql/arcanist,haskell-infra/arcanist,haskell-infra/arcanist,jra3/arcanist,calblueprint/arcanist,hach-que/arcanist,chundongwang/arcanist,KieranHayes/arcanist,kevinseelbach/arcanist,wikimedia/phabricator-arcanist,haskell-infra/arcanist,Khan/arcanist,calblueprint/arcanist,dguo-coursera/arcanist,codelabs-ch/arcanist,Khan/arcanist,fivestars/arcanist,PageUpPeopleOrg/arcanist-patches,fivestars/arcanist,KieranHayes/arcanist,eSpark/arcanist,sneakpeeq/arcanist,jra3/arcanist,wikimedia/phabricator-arcanist,wikimedia/phabricator-arcanist,coursera/arcanist,wxstars/arcanist,jra3/arcanist,julkiewicz/arcanist,eSpark/arcanist,zhihu/arcanist,aik099/arcanist,phacility/arcanist,julkiewicz/arcanist,memsql/arcanist,hach-que/arcanist,memsql/arcanist,phacility/arcanist,haskell-infra/arcanist,fivestars/arcanist,alexmv/arcanist,chundongwang/arcanist,r4nt/arcanist,sneakpeeq/arcanist,codelabs-ch/arcanist,alexmv/arcanist,alexmv/arcanist