merge default into bug25397
improve assertion in vq:fold test
much more thorough testing of vq:requeue
improving code coverage
test
filter out pending acks when folding over delta
merge degault into bug25397
merge bug25400 into bug25397
which is rather conflict-ridden; essentially requiring the rewriting
of the crux of the change in bug25400 in the context of new iterator.
merge default into bug25395
merge bug25397 into bug25395
which involved tweaking the variable_queue_with_holes result slightly,
and ripping out a whole bunch of now-redundant test code.