Workaround needed on mac

[brodycj]

need to do this for now:

diff --git a/tests/compiletest/mod.rs b/tests/compiletest/mod.rs
index f4e26c1..42ec349 100644
--- a/tests/compiletest/mod.rs
+++ b/tests/compiletest/mod.rs
@@ -34,7 +34,7 @@ pub fn contains_panic(name: &str, code: &str) -> bool {
         .arg("--out-dir")
         .arg(tempdir.path())
         .arg("--extern")
-        .arg("no_panic=target/debug/libno_panic.so")
+        .arg("no_panic=target/debug/libno_panic.dylib")
         .status()
         .expect("failed to execute rustc");
     assert!(status.success());

should be easy to fix :=)