• Fixed: Issue 21: typos causing errors
• Fixed: Issue 23: Comma's between methods in Allow header.
• Added: Sabre_DAV_ICollection interface, to aid in future compatibility.
• Added: Sabre_DAV_Exception_Forbidden exception. This will replace
  Sabre_DAV_Exception_PermissionDenied in the future, and can already be used to
  ensure future compatibility.