一直碰到一个AVUser更新自己的数据，报 206. 做了很多测试，发现，如果先做login, 然后再更新数据，没问题。如果程序被杀死了，或者手机重启了，就一定会有问题。 尝试打印了一下刚刚login成功， 和 手机重启后的currentUser()对象，发现如果杀掉程序然后再启动，或者重启手机后再启动程序，currentUser()丢失了很多字段，包括sessionToken; 而且还有别的字段变化，比如 authenticated: 由true变成了false. log如下： 求解释。
03-14 18:34:11.491 32229-32229/com.beecloud.beecloud I/BeeCloud: [1] LaunchActivity.onCreate: current user is:{"@type":"com.beecloud.beecloud.model.bean.User","anonymous":false,"authenticated":true,"avatarUrl":"http://pic.wenwen.soso.com/p/20120116/20120116170947-1389148005.jpg","className":"_User","createdAt":"2016-03-09T21:53:18.192Z","dataAvailable":false,"fetchWhenSave":true,"installationIds":["338d2d6e3db31c680af32cba6c2b5033","bff9ecdbda83e7cf78c2611a8ac3310b"],"mobilePhoneVerified":false,"nick":"未指定昵称","objectId":"56e02aceda2f60004cd5e410","sessionToken":"s8ri13ynwowf89drgvo9e1tmy","type":1,"updatedAt":"2016-03-10T18:30:57.080Z","username":"sj2","uuid":"5d4c29a7-c773-49fd-9b7b-0579cab2d0cb"}
03-14 18:34:29.251 4795-4795/com.beecloud.beecloud I/BeeCloud: [1] LaunchActivity.onCreate: current user is:{"@type":"com.beecloud.beecloud.model.bean.User","anonymous":false,"authenticated":false,"avatarUrl":"http://pic.wenwen.soso.com/p/20120116/20120116170947-1389148005.jpg","className":"_User","dataAvailable":false,"fetchWhenSave":false,"mobilePhoneVerified":false,"nick":"未指定昵称","objectId":"56e02aceda2f60004cd5e410","type":1,"username":"sj2","uuid":"40b7856f-0b30-49f1-87b1-296f64b278ee"}
