Allow unstable warnings during tests

Author: alexcrichton

src/lib.rs

@@ -14,6 +14,7 @@
        html_favicon_url = "http://www.rust-lang.org/favicon.ico",
        html_root_url = "http://doc.rust-lang.org/rustc-serialize/")]
 #![cfg_attr(test, deny(warnings))]
+#![cfg_attr(test, allow(unstable))]
 
 // test harness access
 #[cfg(test)]