104baab5 fixed double-counted pageviews for the initial page load. Under the default 'loading slider' implementation, that resolved all the known problems.
However, under the 'loading spinner', there is an additional problem. In 'spinner' mode, each navigation within the JS app involves transitioning to an intermediate 'loading' route. Previously, this intermediate state was being treated as a separate page by the app, and so any ajax requests fired during it would be counted as a distinct pageview. One known case of this is the `/presence/get` request which is made when logged-in users visit a topic.
This commit updates the logic to ignore 'intermediate' transitions, and introduces regression tests for both the 'spinner' and 'slider' modes.
f3cc294470