原因：
最新的api出了一个这样的内容
adb_has_moved.txt
The adb tool has moved to platform-tools/If you don't see this directory in your SDK,launch the SDK and AVD Manager (execute the android tool)and install "Android SDK Platform-tools"Please also update your PATH environment variable toinclude the platform-tools/ directory, so you canexecute adb from any location.
导致我下载不了api，更新出现问题。
解决办法如下：
1、install new software 将ADT更新网址由https://dl-ssl.google.com/android/eclipse
强制改为http://dl-ssl.google.com/android/eclipse
2、然后进入sdk manager，选择tools，把下面的勾全选上。
