toArray with includedForeignObjects should not prefix the arrays of foreignObjects

Fix for #649 and #648

Now the result of toArray is much more natural. You expect the foreign-objects to have a numeric index instead of being prefixed with the foreign-object-name.

`$book->toArray(...);` before this pr:
```
(
    [Id] => 
    ....
    [Reviews] => Array
        (
            [Review_0] => Array
                (
                    [Id] => 
                    ....
                )

        )

)
```

After this pr:
```
(
    [Id] => 
    ....
    [Reviews] => Array
        (
            [0] => Array
                (
                    [Id] => 
                    ....
                )

        )

)
```