Add xfailed test case for issue 2611

Author: catamorphism

src/test/run-pass/issue-2611.rs

@@ -0,0 +1,11 @@
+// xfail-test
+import iter;
+import iter::base_iter;
+
+impl Q<A> for base_iter<A> {
+   fn flat_map_to_vec<B:copy, IB:base_iter<B>>(op: fn(B) -> IB) -> [B] {
+      iter::flat_map_to_vec(self, op)
+   }
+}
+
+fn main() {}