Clean rebase of 1693

[Aaronontheweb]

Original commit message:

Have depended upon current implementations enumerable over values collections being in ascending order following a load of tests on the collections i performed elsewhere. This is not explicitly documented - but does follow the standard 'walk tree' behavior so is perhaps dependable.

I did not write any of this code - all credit is due to @MrTortoise.

All I did was use my git super powers to squash the commits on #1693

[Aaronontheweb]

Referencing the original issue too: #1676

[maxwellb]

Bah, I commented in #1698 -- there's only 5 of them ;-)

The API changes look good. I ran Performance through NBench.. some tests have standard deviations thinner or wider, but averages/maxes don't seem to jump up in any alarming increments.

https://gist.github.com/maxwellb/c1eb44422427a52fa015

As noted in the gist, there is one failing test when I ran, but it was failing on dev, too, so ymmv?