Update some compile-fail tests to accommodate new scoping/dtor rules.

Author: pnkfelix

src/test/compile-fail/borrowck-borrowed-uniq-rvalue.rs

@@ -16,10 +16,11 @@ extern crate collections;
 use std::collections::HashMap;
 
 fn main() {
+    let tmp;
     let mut buggy_map: HashMap<usize, &usize> = HashMap::new();
     buggy_map.insert(42, &*box 1); //~ ERROR borrowed value does not live long enough
 
     // but it is ok if we use a temporary
-    let tmp = box 2;
+    tmp = box 2;
     buggy_map.insert(43, &*tmp);
 }

src/test/compile-fail/issue-18783.rs

@@ -13,8 +13,8 @@
 use std::cell::RefCell;
 
 fn main() {
-    let c = RefCell::new(vec![]);
     let mut y = 1us;
+    let c = RefCell::new(vec![]);
     c.push(box || y = 0);
     c.push(box || y = 0);
 //~^ ERROR cannot borrow `y` as mutable more than once at a time