So, for 'to' fields too, we use two separate data structures: binary
search trees (BST) for exact match and linked lists for substring match.
Now all 'from' and 'to' fields in filtering rules use these two data
structures.
To repeat, filtering rules should be written with exact matches instead
of substring matches, as much as possible. Because BST search must be
much faster than substring search over linked lists.
To repeat, we have modifed kbtree to support complex data structures in
from fields.
Also, update the unit tests accordingly.
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