Make oneshot pipes work again

[brson]

oneshot pipes don't work reliably and as a result aren't used in very many places where they should be. Add a bunch of test cases and make this work correctly again.

I don't have any specifics but when I've used them there were assertions failures.

[metajack]

Is this still relevant with the new scheduler?

[brson]

Thte problem here was by-val self. Obsolete now.