Add a linter rule for the instanceof operator

Summary: The instanceof operator expects the first argument to be an object instance. See http://www.phpwtf.org/instanceof-smart.

Test Plan: Added test case

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12856