Add two tests for rvalue mutability

src/test/run-pass/borrowck-rvalues-mutable.rs

@@ -0,0 +1,30 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Counter {
+    value: uint
+}
+
+impl Counter {
+    fn new(v: uint) -> Counter {
+        Counter {value: v}
+    }
+
+    fn get_and_inc(&mut self) -> uint {
+        let v = self.value;
+        self.value += 1;
+        v
+    }
+}
+
+pub fn main() {
+    let v = Counter::new(22).get_and_inc();
+    assert_eq!(v, 22);
+}