elm elm_widget.c: Added elm_widget_sub_object_add() parameter

elm elm_widget.c: Added elm_widget_sub_object_add() parameter
verification. Patch by Taehwan Kim <ohpowel@gmail.com>

On Tue, Apr 10, 2012 at 5:37 PM, Bluezery <ohpowel@gmail.com> wrote:
> Hello,
>
> Currently, elm_widget_sub_object_add() does not check if obj and sobj
> are same object.
> Actually it is a user problem if user add object itself as it's sub
object.
> But I think that this checking is needed and it is better to give
> error logs to users.  Because it causes infinite loop and it is hart
> to debugging.  :(
>
> Thanks.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/elementary@69995 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33