BACKPORT-NOTES.txt

* Need to use Python 3.6 version of Argument Clinic

From CPython checkout:

    git checkout 3.6 -- Tools/clinic/

then:

    ./python Tools/clinic/clinic.py Modules/_pickle.c
    cp Modules/clinic/_pickle.c.h ../pickle5-backport/pickle5/clinic/_pickle-3.6.c.h

* Same for 3.5 and 3.7

* Currently, we are syncing with cpython v3.8.3

* For python3.5, we skip tests for __getnewargs_ex__ when protocol < 4, because it is not supported. We also skip numpy array tests, because the current numpy version doesn't support pickle protocol 5.