def role_listing
      xml   = make_xml('RoleListingRequest')
      r     = execute(xml, '1.2')
      roles = []
      if r.success
        r.res.elements.each('RoleListingResponse/RoleSummary') do |summary|
          roles << RoleSummary.parse(summary)
        end
      end
      roles
    end
def role_listing
      xml   = make_xml('RoleListingRequest')
      r     = execute(xml, '1.2')
      roles = []
      if r.success
        r.res.elements.each('RoleListingResponse/RoleSummary') do |summary|
          roles << RoleSummary.parse(summary)
        end
      end
      roles
    end
Returns a summary list of all roles.