Test needs to clean up cookies for all paths used

Browsers don't support clearing cookies unless you know the exact path.

This fixes the test failures I see when running the test more than once
(I had to clear cookies once in advance, because I've renamed the paths.
The new path names will be easier to remember in case they're used in more
than one test in future).

I'm running the test from file:/// at the moment, but AFAIK this is a
general limitation.