Make words that were ignored available to the caller (for displaying).

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Need to check sorting algorithm for compliance with the problem pointed
out by Andrey Tarasevich in z1. That is that order of elements equal
from the point of view of sorting algorithm is the same in all keywords
id lists. Otherwise joining will not work properly.

One possible solution is to sort all ids first and then keep that order
in all lists that are then by definition subsets of it.