Test for #876

This is the test case for #876. Xfailed for now.

src/test/compile-fail/tag-that-dare-not-speak-its-name.rs

@@ -0,0 +1,10 @@
+// -*- rust -*-
+// xfail-test
+// error-pattern:mismatch
+use std;
+import std::vec::*;
+
+fn main() {
+    let y;
+    let x : char = last(y);
+}