`copy` and `send` ifaces cannot be used as type parameter bounds

[brson]

While ifaces with the name copy and send can be declared and implemented, they are always shadowed by the copy and send kind bounds when used like fn f<T: send>. A small inconsistency.

iface send {
    fn f();
}

fn f<T: send>(t: T) {
    t.f();
}

fn main() {
}

../src/test/run-pass/test.rs:6:4: 6:7 error: attempted access of field f on type 'a, but no public field or method with that name was found
../src/test/run-pass/test.rs:6     t.f();
                                   ^~~
../src/test/run-pass/test.rs:6:4: 6:9 error: the type of this value must be known in this context
../src/test/run-pass/test.rs:6     t.f();
                                   ^~~~~

[marijnh]

Does disallowing these words as iface names sound like an acceptable solution?

[catamorphism]

We won't disallow these words as trait names, now that copy and send are just traits. But, I'll fix the code so it doesn't prioritize copy and send over a user-defined trait shadowing one of these names.

[catamorphism]

Still a bug as of a477c5a.

[catamorphism]

Fixed, pending code review by @nikomatsakis .