The "runnableExample.template.html" template overrides the one in the
dgeni-packages "examples" package with a similar template that also has
a link to a special Plunker URL that can pull in the example from our
code.angularjs.org website.
Before we were simply sending the current location, but multiple URLs map
to the same document.
Now, we use the canonical path of the current document if available and
fall back to the $location path otherwise.
Includes tests!!
Closes#6402
