Test harness inserts unstable warnings

[seanmonstar]

With a file like:

pub struct Foo;
impl Copy for Foo {}

And then running rustc --test test.rs, these warnings are inserted:

sean@grunt:~/code$ rustc --test test.rs
<command line option> warning: use of unstable item: will be replaced by slice syntax, #[warn(unstable)] on by default
test.rs:1 pub struct Foo;
          ^
<command line option> warning: use of unstable item, #[warn(unstable)] on by default
test.rs:1 pub struct Foo;
          ^
<command line option> warning: use of unstable item, #[warn(unstable)] on by default
test.rs:1 pub struct Foo;
          ^

cc @alexcrichton @aturon

[alexcrichton]

I believe @brson was working on this.

[alexcrichton]

Nominating though, when we deny warnings in beta I've gotta be able to test my code still!

[seanmonstar]

I've been using #[cfg_attr(test, deny(warnings))], and this blocks me from testing. For now, I have to comment out that line...