Bug#945389: skimage: FTBFS with python3.8 (test failures)

[Ole Streicher]

Control: tags -1 pending

Hi Andreas, Stefan,

the error message "no attribute '__reduce_cython__'" was actually
misleading. The problem here was that the required test files were not
installed in the .build directories. This had two causes:

1) the PYBUILD_VERSIONS variable is not set automatically, but is rather
an input to control the versions to be built

2) The files need to be copied and not just linked. Linking somehow
confuses pytest.

I am going to fix this (and the other problems) and plan to upload the
new version to unstable ASAP (today or tomorrow).

Let's hope that it doesn't break other's CI tests!

Cheers

Ole