Add another unwind test

This makes sure that cleanups added after the first invoke in a scope are
actually run on unwind

src/test/run-fail/unwind-interleaved.rs

@@ -0,0 +1,12 @@
+// error-pattern:fail
+
+fn a() { }
+
+fn b() { fail; }
+
+fn main() {
+    let x = [0];
+    a();
+    let y = [0];
+    b();
+}