* Ensure every time a file becomes a directory or the other way around
the item is flagged as INSTRUCTION_TYPE_CHANGE.
* Delete the badly-typed entity if necessary in the propagation jobs.
Progress estimation is usually based on transfer speed. That makes no
sense when we're doing operations like deletes, that need very little
data transfer but nevertheless take a long time.
This hack attempts to detect this case better and switches to a
different estimate.
We should rewrite this to maintain and update estimates for the
transfer speed, per-file overhead and chunk-assembly overhead each
time an item finishes. Then we could provide more consistent progress
estimates without ad-hoc fixes like this one.
Also, there's an issue where resuming a partial download will lead
to exaggerated transfer speed estimates.
