Add "--revision <id>" flag to "arc land"
Add "--revision <id>" flag to "arc land"

Summary: Allow the user to pick a revision explicitly if they think they know what they're doing. Similar to "arc amend --revision", etc.

Test Plan: Obviously compells a meta-test.

Reviewers: btrahan, fratrik

Reviewed By: fratrik

CC: aran, epriestley

Maniphest Tasks: T928

Differential Revision: https://secure.phabricator.com/D1753

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