Add a routine in our tests that recursively visits each link in the admin bar and checks for fatals/WSODs

[klonos]

I don't know the internals of our testing framework, so I can't really tell if this is possible at all, but this idea came to me because of the fatals @serundeputy and myself were coming by as we tested various things in #87...

If there was a way to automate visiting all available links in admin bar (at the very least) and made sure they don't return fatals or WSODs, we'd be able to catch bugs sooner. So, can we?

[quicksketch]

The troubles we experience in #86 were a little bit of exceptional situations, where the WSODs were caused by both a contrib and core version of Token module being loaded at the same time. We already have tests that load the Pathauto interface, lots that use the node form, and a few that check the status report, but none of these were failing because the WSODs required a set of conditions outside core itself.

We should have tests on every one of the pages in the admin bar individually, not just to check that they don't WSOD, but that the functionality in them actually works. So I don't think adding this check would actually solve much by itself (it wouldn't have prevented any issues in #86 at least) and we should work to continue expanding our test coverage one form at a time where necessary (though this also won't help prevent the problems in #86).