Remove score_evenness() functions in matchspy.h

[Richard Boulton]

The score_evenness() functions in matchspy.h were intended to be a way to determine how good a particular set of facet results is. However, after experience using the facet support in real-life situations for a couple of years, I'm very dubious that they ever give useful results: each time I've tested them out, the choice of facets produced by score_evenness() has been pretty poor: a manual fixed choice of order of facets has always been an improvement.

It's possible that the calculation from score_evenness() might be useful in some situations I've not come across, but it's not hard to implement an equivalent outside Xapian.

I therefore propose to move the score_evenness() functions out of Xapian trunk. I'd leave them on the MatchSpy branch for now, but if we've not found a real use for them by the time we've worked out a clean API for the MultiValueCountMatchSpy, I think we can drop them.

[Olly Betts]

Seems reasonable. Don't forget to remove it from categorisation.rst.

[Richard Boulton]

Removed from trunk in r13883. Leaving it in limbo on the matchspy branch for now: now's the time for anyone who misses it to ask for its resurrection, but marking this ticket as closed since I'll be stunned if anyone does.