Add cfail test arc-rw-state-shouldnt-escape

src/test/compile-fail/arc-rw-state-shouldnt-escape.rs

@@ -0,0 +1,11 @@
+// error-pattern: reference is not valid outside of its lifetime
+use std;
+import std::arc;
+fn main() {
+    let x = ~arc::rw_arc(1);
+    let mut y = none;
+    do x.write |one| {
+        y = some(one);
+    }
+    *option::unwrap(y) = 2;
+}