Chrome: Streamline redirect counter

(For issue #12)

This refactors & optimizes the old redirect counter.

The redirect counter exits to catch infinite HTTPS <-> HTTP loops. The old counter
was messy, constantly churning a small array of requestIds. I think it was written
before the new API call: onBeforeRedirect.

(The old counter also generated a lot of orphan entries, e.g. when another
extension or the browser itself aborted requests / redirected to about:blank.)

Signed-off-by: Nick Semenkovich <semenko@alum.mit.edu>
Merge pull request #199 from semenko/redirect-tweak

Chrome: Streamline redirect counter