added an insert method

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4887 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/util/ArrayUtil.as

@@ -144,6 +144,19 @@ public class ArrayUtil
         return true;
     }
 
+    /**
+     * Inserts the element into the array at the given index, increasing the index on all 
+     * remaining elements by one.  This function modifies the array passed in, rather than creating
+     * a new one.
+     */
+    public static function insert (arr :Array, index :int, element :Object) :void
+    {
+        for (var ii :int = arr.length; ii > index; ii--) {
+            arr[ii] = arr[ii - 1];
+        }
+        arr[index] = element;
+    }
+
     /**
      * Implementation of remove methods.
      */