Allow `new self` in linter

Summary: Also allow `sTaTiC::$x` which is a valid PHP (contrary to `sElF::$x` which is invalid PHP but I allowed that too).

Test Plan:
  new self;

Reviewers: epriestley

Reviewed By: epriestley

CC: wez, aran, Korvin

Differential Revision: https://secure.phabricator.com/D5241