The test tests/fixtures/reftests/svg1.1/pservers-grad-16-b.svg was not
passing.

This test has gradient stop offsets in the wrong order.  Cairo
automatically sorts them, but the SVG spec mandates that they should be
adjusted to be in nondecreasing order.

I was actually confused two commits ago; I thought the spec mandated
that the stop offsets were invalid if they weren't ordered.