#288 Galago: FlattenCombineTraversal loses combine NodeParameters (e.g. norm=false, scorer=bm25)

[John Foley]

This was discovered by Keping while working on Rocchio. As a workaround, she sets "flattenCombine=false" in her query parameters, but this traversal should maybe give up if it hits negative weights or norm=false, since it applies a norm as it goes (usually fine, since norming will be ranksafe) but explicitly not what the user wants when the have:

#combine(a b #combine:norm=false(c d))

It will take the weights on c and d and norm them before sticking them into the upper-level combine. Basically, if a child has a norm=false, it should give up.

Small change, but will need tests.