Use base fixture from tar to prevent permission problems

[Vampire]

At least on Cygwin there were problems when the files in the base fixture were
created by a Git checkout, as Git does not care about permissions besides
executable flag.
But for the SVN repo properly functioning, permissions seem to be crucial.
So now the base fixture is extracted from a tar archive instead.

[Vampire]

@tnyblom do you prefer the single PRs I posted now and I rebase after you merged (because conflicts in test files), or do you want me to combine all in one PR?

[tnyblom]

@Vampire What ever you like :)

[Vampire]

Well, I'm currently done with changes, unless I find another bug during the conversion I'm currently doing. :-)

[Vampire]

Argh, please wait with further merges, except for this one here which is safe.
I combined my PRs and used it and it greatly misbehaves.
I'll investigate later where I fucked up.

[Vampire]

You can continue merging my PRs, the one that breaks it is #96 and I pushed a test that fails so you do not merge it accidentally.
Btw. in the settings of the GitHub repo you can require that the check be successful for merging.

[Vampire]

Ok, #96 should be correct too now. :-)

[katanacrimson]

FWIW, this PR causes all tests to fail when building a docker image using the dockerfile in the repository. It appears that the version of tar that ships with Debian 8.11 is too old to support --one-top-level.

[katanacrimson]

Actually, looking further, it looks like the tests were never utilized in conjunction with the dockerfile (which predates them) at all. Nevermind me!