Cleanup order semantic

[ Edit by Mathieu Desnoyers: renamed "end_order" to "last_order", to
  match the "first_order" inclusive semantic. Normally, "end" excludes
  the range limit value, but "last" includes it. We use an inclusive
  range end value here. ]

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>