[Libguestfs] [PATCH libnbd v2 0/3] python: Add test for doing asynch copy.

v1 was here: https://www.redhat.com/archives/libguestfs/2019-August/msg00103.html In v2 I've made several changes: - Fix Python callbacks so if they don't return something which is int-like, we assume they mean to return 0. - Add nbd.Buffer free() method. Read commit message in patch 2 to see what this is about. - Fixed the asynch copy test to deal with the unbelievably braindead behaviour of Python closures. It took me many hours this morning to work out what was going on. It turns out that Python closures aren't closed (yeah, the clue is in the name, Python developers). Rich.