Restore "arc patch D12345" syntax
Restore "arc patch D12345" syntax

Summary:
I only dropped this because it's slightly inconvient to accommodate, but
empirically it's pretty confusing to users (who often use --diff 12345 when they
mean --revision 12345).

Test Plan:
Ran "arc patch D45", "arc patch --revision 45", "arc help patch"

Reviewed By: tuomaspelkonen
Reviewers: tuomaspelkonen, jungejason, aran
CC: aran, tuomaspelkonen
Differential Revision: 241

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