auto merge of #7113 : alexcrichton/rust/banned-warnings, r=cmr

Reopening of #7031, Closes #6963

I imagine though that this will bounce in bors once or twice... Because attributes can't be cfg(stage0)'d off, there's temporarily a lot of new stage0/stage1+ code.

src/libstd/task/spawn.rs

@@ -91,7 +91,7 @@ use uint;
 use util;
 use unstable::sync::{Exclusive, exclusive};
 use rt::local::Local;
-use iterator::{IteratorUtil};
+use iterator::IteratorUtil;
 
 #[cfg(test)] use task::default_task_opts;
 #[cfg(test)] use comm;