For some reason the tree-shaker is not picking up these interfaces
(perhaps TS is not passing it through) when they are in the same file
as their related services. This results in a distracting warning message.
There is a weirdness in the Angular Location service.
If the `baseHref` is only a single slash (`'/'`) then it
changes it to be an empty string (`''`). The effect of this
is that `Location.normaliseUrl(url)` does not strip off the
leading slash from url paths.
The problem is that the leading slash only appears on the
initial Location path, and not on urls that arrive from subscribing
to the Location service.
This commit is a workaround this problem.
