Complain about Reuse of By-ref Iterators

Summary:
Added a lint rule that warns about reusing iterator reference
variables.

Test Plan:
- Add a file with examples found in with https://secure.phabricator.com/T2536
- Did not make a unit test yet

Reviewers: vrana, bill, epriestley

Reviewed By: epriestley

CC: aran, epriestley, Korvin

Maniphest Tasks: T2536

Differential Revision: https://secure.phabricator.com/D5179