Tweak debugging printf.
WIP test case for poset.
Support accumulate_tick_deltas mode for poset collections.
Rename test file for posets.
Fix another bug with delta processing for poset.
Add another poset test case.
Fix another bug in delta processing for posets.
Tweak debugging printf.
More win-move tests.
Add common debugging tool for poset query eval.
Implement po_scratch collection type.

This is similar to a poset, but provides scratch-like transient/view
semantics. We should probably rename poset to po_table for consistency.
Add another po_scratch test case.