http://blog.csdn.net/astrotycoon/article/details/41172389
wait函数返回值总结
http://www.cnblogs.com/Anker/p/3271773.html
wait函数返回值总结，孤儿进程与僵尸进程[总结]
原文：http://www.cnblogs.com/LiuYanYGZ/p/5789545.html
