Slightly optimize ApproximateBestSubset and its usage for PS txes#3184

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UdjinM6 merged 3 commits intodashpay:developfrom

UdjinM6:tweakbestsubset

Nov 4, 2019

Commits on Oct 31, 2019

From 2 best sets with the same `nTotal` in ApproximateBestSubset prefer the one with less inputs
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There is no reason to run ApproximateBestSubset again if nMinChange is 0
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Commits on Nov 4, 2019

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