Selector order not preserved when extending

[eevee]

Ruby:

a { color: red; }
b { @extend a; }
# a, b { color: red; }

vs

b { color: red; }
a { @extend b; }
# b, a { color: red; }

We naïvely sorted the selectors, producing a, b in either case.

[eevee]

I can't think of any case where this would actually matter semantically. But it would be nice. :)

[eevee]

This is now fixed, barring a particular edge case that's covered by the imported Ruby test suite.