Fix webdav lock with Office 2007 (document opened read only)

According to this specification : http://www.webdav.org/specs/rfc4918.html#rfc.section.15.8.1
D:owner element could not contain a d:href element.
(<!ELEMENT owner ANY >)

As suggested in this issue, http://oss.101tec.com/jira/browse/WDS-22, removing the 'd:href'
element fix read only bug with office 2007.

I'm not really sure about the fix, but it's fixes document editing with both office 2007 and
office 2010 under windows 7.