Improve the robustness of the "alias function" linter rule

Summary: Improve the ArcanistXHPASTLinter::LINT_ALIAS_FUNCTION linter rule. Currently this rule does not correctly handle alias functions which are not strictly lowercase.

Test Plan: Added a test case.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12921