def folder_id!(fid, change_key = nil)
      attribs = {'Id' => fid}
      attribs['ChangeKey'] = change_key if change_key
      @nbuild[NS_EWS_TYPES].FolderId(attribs)
    end
def folder_id!(fid, change_key = nil)
      attribs = {'Id' => fid}
      attribs['ChangeKey'] = change_key if change_key
      @nbuild[NS_EWS_TYPES].FolderId(attribs)
    end
Build the FolderId element
 @see http://msdn.microsoft.com/en-us/library/aa579461.aspx