Respect rem-with-px-fallback in CSS3 output

[rctneil]

In regards to the rem-with-px-fallback flag.

If someone has this set to 1 then will future versions of things, such as (for example) border radius adhere to this and output appropriate CSS in rem and then with a pixel fallback?

[mirisuzanne]

That seems like the way it should work. I'll look into it. That might be as simple as passing prefix-prop output through the rem mixin, unless @chriseppstein wants to build rem-fallback in as a global output feature somehow.