Merge pull request rust-lang#388 from JakubOnderka/patch-1

Fix build for beta and nightly.

Since it's truly unused, I wonder if it rather should be removed then allowed, but the comment on the module makes me think there is some deeper purpose. So better play it safe.

src/ffi/c.rs

@@ -359,6 +359,7 @@ pub use self::c_backend::*;
 
 /// For backwards compatibility, we provide symbols as `mz_` to mimic the miniz API
 #[allow(bad_style)]
+#[allow(unused_imports)]
 mod c_backend {
     use std::mem;
     use std::os::raw::{c_char, c_int};