GetSampleText.java: API 18 provides a constant for the 'sampleText' return value, so use it

android/src/com/reecedunn/espeak/GetSampleText.java

 /*
- * Copyright (C) 2012 Reece H. Dunn
+ * Copyright (C) 2012-2013 Reece H. Dunn
  * Copyright (C) 2011 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
 
         final int result = TextToSpeech.LANG_AVAILABLE;
         final Intent returnData = new Intent();
-        returnData.putExtra("sampleText", text);
+        returnData.putExtra(TextToSpeech.Engine.EXTRA_SAMPLE_TEXT, text);
         setResult(result, returnData);
         finish();
     }