to_xml with :include should skip_instruct on the included records

When calling e.g. record.to_xml(@person, :include => [:company]) the xml output has multiple xml instruct elements. For example:

<?xml version="1.0" encoding="UTF-8"?>
<company>
  <name>Company A</name>
  <id>662</id>
  <people>
    <inspect/>
    <?xml version="1.0" encoding="UTF-8"?>
    <person>
      <name>Person A</name>
      <id>677</id>
    </person>
    <inspect/>
    <?xml version="1.0" encoding="UTF-8"?>
    <person>
      <name>Person A</name>
      <id>677</id>
    </person>
  </people>
</company>

Attached patch fixes this.