collections: grow should use the overflow-checked reserve_additional

Author: erickt

src/libcollections/vec.rs

@@ -253,8 +253,7 @@ impl<T: Clone> Vec<T> {
     /// assert_eq!(vec, vec!("hello", "world", "world"));
     /// ```
     pub fn grow(&mut self, n: uint, value: &T) {
-        let new_len = self.len() + n;
-        self.reserve(new_len);
+        self.reserve_additional(n);
         let mut i: uint = 0u;
 
         while i < n {