Deprecated re-exports are ignored

The following code compiles with no warnings, even though it should emit a deprecation warning. Both Diesel and Futures have mistakenly used this to deprecate items moved to a new location, without realizing that users would never see a deprecation warning.

```rust
pub mod foo {
    #[deprecated(since = "0.1.0")]
    pub use std::option::Option;
}

mod bar {
    use foo::Option;
}
```

  