Declares whether your application is willing to support right-to-left (RTL) layouts.If set to true and targetSdkVersion is set to 17 or higher, various RTL APIs will be activated and used by the system so your app can display RTL layouts. If set to false or if targetSdkVersion is set to 16 or lower, the RTL APIs will be ignored or will have no effect and your app will behave the same regardless of the layout direction associated to the user's Locale choice (your layouts will always be left-to-right).The default value of this attribute is false.This attribute was added in API level 17.
声明你是否支持从右到左（right-to-left ）的布局形式，如果设置true并且targetSdkVersion>=17,
各种各样的RTL apis将会起作用，你的app会展示PTL布局
如果设置false或者targetSdkVersion<17（安卓4.2），RTL apis将不在起作用，即使选择你的地区，不管怎么样，你的布局始终从左向右。
默认值是false。
这个属性在api17版本加入。
