duplicate add buttons on collections when about is duplicated

[David Buchmann]

if the about attribute is duplicated, i.e. in the entity itself and in a list container of the collection, the add button is duplicated.

<div about="/cms/simple/news" xmlns:sioc="http://rdfs.org/sioc/ns#" xmlns:dcterms="http://purl.org/dc/terms/" xmlns:skos="http://www.w3.org/2004/02/skos/core#" typeof="mystuff">

    <h2  property="dcterms:title">News</h2>
    <p  property="sioc:content">The latest news about the Symfony CMF:</p>

    <ul  rel="dcterms:hasPart" rev="dcterms:partOf" about="/cms/simple/news">
        <li  typeof="sioc:Post" about="/cms/simple/news/symfony-cmf-website-update">
                <div property="dcterms:title">Symfony CMF website update</div> (2012-09-28)
                <div class="newscontent" property="sioc:content">A test news</div>
        </li>
    </ul>
</div>

@flack says @bergie wants to fix this behaviour and it is a VIE bug in openpsa/createphp#27