Add example co-inductive/mutual recursion issues with trait

Author: cmester0

examples/coverage/src/lib.rs

@@ -9,3 +9,5 @@ mod test_closures;
 mod test_functions;
 
 mod test_instance;
+
+mod test_trait;

examples/coverage/src/test_trait.rs

@@ -0,0 +1,11 @@
+// Broken..
+
+// // Co-inductive trait
+// trait TraitA {
+//     type B : TraitB;
+// }
+
+// trait TraitB {
+//     fn test<U>(other : U) -> U
+//     where U: TraitA;
+// }