fix cached request issue

Hi,
I think I've been having the same issue, and this is what I think is going on.

The issue is in promise-tracker-http-interceptor. Deferred promises are referenced by request config. That's fine, except when a request is configure with option cache = true. Let's say we have a request like that, the first time the request is sent, a promise will be created and its response will be cached. Next time the same request is sent, a new promise will be created but the $http will return the cached response which contains a reference to the first promise already resolved

Please see here a plunker http://plnkr.co/edit/66daaWDq7IUdbJmfP4oq I'll do a pull request