DUBBO-523 停机时线程池关闭空指针
DUBBO-524 内嵌jetty服务器没有绑定anyhost
添加UT DUBBO-519 ExtensionLoader的getExtension方法在没有扩展时抛出异常，而不是返回null
Activate添加JavaDoc
update javadoc
Merge remote-tracking branch 'origin/master'
update activate javadoc
DUBBO-528 修改兼容性判断
Merge branch 'master' of https://github.com/alibaba/dubbo
强加可见性
DUBBO-530 ExtensionLoader加载失败后，之后调用抛的异常没有当时调用的栈
Merge remote-tracking branch 'origin/master'
DUBBO-531 registry标签增加cluster属性便于配置
Merge branch 'master' of https://github.com/alibaba/dubbo
DUBBO-512 排除不必要的URL属性
DUBBO-512 ExtensionLoader支持编程方式添加扩展
Merge remote-tracking branch 'origin/master'
DUBBO-527 Remoting的异常不应显示服务名
DUBBO-532 修复心跳不兼容问题
DUBBO-532 修改日志