XHProf: add .arclint, fix some minor issues

Summary: Add a .arclint file and fix some stray tabs and whitespace issues.

Test Plan: Built xhprof, ran tests (some failures, but preexisting).

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10372