Steps to reproduce the issue

In Joomla administration, open an article while having TinyMCE set as editor in extended mode.
Click the insert/edit link button in the MCE toolbar.

Expected result

In most sites, when users insert a link it is rarely the case that a rel attribute is needed, and in only a fraction of those cases will the user be linking to an alternate version of the current piece of content.
There should be a "None" option for the rel field and it should be the default.

Actual result

The Rel attribute dropdown will default to "alternate" when adding a link.
It is impossible to not set a rel attribute

System information (as much as possible)

Joomla 3.x, TinyMCE editor, extended

Additional comments

This can be fixed by adding array('title' => 'None', 'value' => ''), as the first element of the $scriptOptions['rel_list'] array in /plugins/editors/tinymce/tinymce.php