Summary: Creates a new base class for unit testing `ArcanistExternalLinter` subclasses. Specifically, add a test case for verifying that we are correctly parsing the output of `$external_linter --version`.
Test Plan: `arc unit`
Reviewers: chad, #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D11197
Summary: This is a bit magical and is maybe a terrible idea, but it seems okayish.
Test Plan: `arc unit`
Reviewers: chad, #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D11172
Summary: Modernize `ArcanistJSHintLinter` by extending from `ArcanistExternalLinter` instead of `ArcanistLinter`.
Test Plan: Wrote and executed unit tests.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D8965
