Menu item aliases changed even if there is no need

Menu item aliases are being changed, even if Joomla has no issues or conflicts. This happens when there are 2 menu items with the same aliases but having different parent.

Quickest fix would change the array to be multi-dimensional (without looking into the code):

```
$aliases[$item->parent] = $item->alias->id;
```

And by checking

```
if (in_array($aliases[$item->parent])) changeAlias();
```
