Fix two linter issues

Summary:
  - The "exclude static variable access" branch in XHPAST incorrectly excluded all variables in a function or method which used any static access (we were selecting the wrong root node for exclusion).
  - The "PHPLinter" regexp did not work with 5.4.30. Make it more permissive in what it parses.

Test Plan:
  - Added a failing unit test for the variable case and made it pass.
  - PHPLinter tests now pass under 5.4.30

Reviewers: joshuaspence, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11087