Data Bucket Stream: fix reindexing
Hello,
please see the details of this MR in the commit messages.
The second patch breaks backwards compatibility.
Since code that relied on the old semantics of __len__ may fail silently, I'd plan for the production instance I take care of, to not deploy it (or only temporarily when reindexing).
However, I still think it's good to add it to upstream Wendelin, as any new project using Data Bucket Stream would benefit from it.
Best, Levin
/cc @Tyagov @paul.graydon @klaus
edit: tests pass