title: ObservableInt causes crash on DataBinding Library
body: <p>I was playing with the new data binding library and tried to implement observable interface . But it keeps crashing no matter if i set the age variable to textview or not.  The code works fine if i convert age variable to String. Is there any way to make it work with int ?  </p>
  
  <pre><code>public class User extends BaseObservable {
  
  @Bindable
  public final ObservableField&lt;String&gt; name =
          new ObservableField&lt;&gt;();
  @Bindable
  public final ObservableInt age = new ObservableInt();}
  </code></pre>
  
  <p>Crash Log : </p>
  
  <pre><code>android.content.res.Resources$NotFoundException: String resource ID #0x3
          at android.content.res.Resources.getText(Resources.java:274)
          at android.widget.TextView.setText(TextView.java:4122)
          at com.hipo.databinding.databinding.ActivityMainBinding.executeBindings(ActivityMainBinding.java:184)
          at android.databinding.ViewDataBinding.executePendingBindings(ViewDataBinding.java:321)
          at android.databinding.ViewDataBinding$6.run(ViewDataBinding.java:160)
          at android.databinding.ViewDataBinding$5.onViewAttachedToWindow(ViewDataBinding.java:130)
          at android.view.View.dispatchAttachedToWindow(View.java:13417)
          at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2707)
          at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2714)
          at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2714)
          at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:2714)
          at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1292)
          at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
          at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
          at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
          at android.view.Choreographer.doCallbacks(Choreographer.java:580)
          at android.view.Choreographer.doFrame(Choreographer.java:550)
          at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
          at android.os.Handler.handleCallback(Handler.java:739)
          at android.os.Handler.dispatchMessage(Handler.java:95)
          at android.os.Looper.loop(Looper.java:135)
          at android.app.ActivityThread.main(ActivityThread.java:5221)
          at java.lang.reflect.Method.invoke(Native Method)
          at java.lang.reflect.Method.invoke(Method.java:372)
          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)public class User extends BaseObservable {
  
  @Bindable
  public final ObservableField&lt;String&gt; name =
          new ObservableField&lt;&gt;();
  @Bindable
  public final ObservableInt age = new ObservableInt();
  </code></pre>
  
  <p>}</p>