[libvirt] pvspinlock not accepted by libvirt

[bancfc at openmailbox.org]

I'm using libvirt version 1.1.3.5 at the moment. I am sure I followed 
the right syntax as I put it under the features section:

<features>
   ...
   <pvspinlock/>
</features>

It says: error internal error: unexpected feature pvspinlock Failed. try 
again?