All performance tests still print to stderr, but do so in a py3 compatible way

There is more work to do though, as many imports are still incorrect.
Also, there are still print statements

This could however, introduce a chance of an assertion hitting once again
as it has been commented out for quite a long time. Now it's back in a changed form
though, and once again tries to make sure we get proper results

[ci skip]

For now, referencing github directly seems to be safest.

It represents the latest state on github, which should be better than
what's installed by default.

[skip ci]