Add xfail'd test for default methods.

src/test/run-pass/traits-default-method-trivial.rs

@@ -0,0 +1,20 @@
+//xfail-test
+
+trait Cat {
+    fn meow() -> bool;
+    fn scratch() -> bool;
+    fn purr() -> bool { true }
+}
+
+impl int : Cat {
+    fn meow() -> bool {
+        self.scratch()
+    }
+    fn scratch() -> bool {
+        self.purr()
+    }
+}
+
+fn main() {
+    assert 5.meow();
+}