Add test for issue #511. Closes #511

Author: brson

src/test/run-pass/issue-511.rs

@@ -0,0 +1,10 @@
+use std;
+import std::option;
+
+fn f<@T>(&o: mutable option::t<T>) {
+    assert o == option::none;
+}
+
+fn main() {
+    f::<int>(option::none);
+}