`hgsubversion` is effectively unmaintained right now. It doesn't work at all with Python 3, and I'm even struggling to get it running on Python 2.7 with older Mercurial releases. Assuming it continues in that state, I don't think many people are using it, and we should probably consider removing it entirely. For now, this change improves our test skipping machinery to prevent failures when we can't successfully clone an SVN repository. Testing Done: Made a temporary change to get things to proceed halfway in the way that they are on some setups (past the basic check for `hgsubversion` but failing when trying to clone. Saw that hgsubversion tests were successfully skipped rather than caused errors.