Remove accept, request, and borrow versions

[Munksgaard]

These functions aren't used any more, confuse users and clutter the namespace.

All occurences of code like

let (tx, rx) = channel();
let t1 = spawn(move || srv(accept(tx).unwrap()));
let t2 = spawn(move || cli(request(rx).unwrap()));

can be replaced by the shorter and nicer

let (c1, c2) = session_channel();
let t1 = spawn(move || srv(c1));
let t2 = spawn(move || cli(c2));

For the tests to still pass, we need to remove the issue-8 compile-fail test, which tested against a soundness bug in request.

[Munksgaard]

This fails because the compile-fail directory does not exist when empty. I'll add a basic compile-fail test.

[Munksgaard]

We could use more of those anyway, to showcase what our library does.

[Munksgaard]

21 will try to add some more tests.

[Munksgaard]

@laumann: r?

[laumann]

r+