ArrayList.addItemAt() behaves like ArrayList.setItemAt()

In my working with ArrayLists I've found that addItemAt is **not** inserting a value, it is **setting** a value...

So:

```
var tableData:ArrayList = new ArrayList();
for( var x:int=0; x<100; x++) {
tableData.addItemAt( value[x], 0 );
}

```
Will produce an ArrayList of only 1 item at position 0...(presuming value is an array 100 length).

Start by locating the ArrayList.addItemAt() and ArrayList.setItemAt() entry points and compare their documented behavior. Reproduce the loop from the issue, then verify that repeated addItemAt(value[x], 0) retains all inserted values rather than replacing the item at position 0.

Written by the indexing model from the issue text.