We need nexedi/ZEO@f2fae122 and nexedi/ZEO@7c104297

Those are small low-risk patches that are all backports of upstream ZEO
master. Upstream declared ZEO4 "dead" and does not want to apply any
patch to 4 branch, so we have to maintain them on our side.

The patches are required for wendelin.core 2 to work correctly because
without them ZEO does not provide full information about committed
objects on invalidation, and so WCFS will provide corrupt file data
because it will miss to know that some part of a file was changed.