Retool the backup process to use a new 'BackupAgent' class

Backups will be handled by launching the application in a special
mode under which no activities or services will be started, only
the BackupAgent subclass named in the app's android:backupAgent
manifest property.  This takes the place of the BackupService class
used earlier during development.

In the cases of *full* backup or restore, an application that does
not supply its own BackupAgent will be launched in a restricted
manner; in particular, it will be using the default Application
class rather than any manifest-declared one.  This ensures that the
app is not running any code that may try to manipulate its data
while the backup system reads/writes its data set.
diff --git a/tests/backup/AndroidManifest.xml b/tests/backup/AndroidManifest.xml
index eaeb5b7..3778742 100644
--- a/tests/backup/AndroidManifest.xml
+++ b/tests/backup/AndroidManifest.xml
@@ -1,6 +1,6 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
         package="com.android.backuptest">
-    <application>
+    <application android:backupAgent="BackupTestAgent">
         <activity android:name="BackupTestActivity" android:label="_BackupTest">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
@@ -8,10 +8,5 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
-        <service android:name="BackupTestService">
-           <intent-filter>
-               <action android:name="android.backup.BackupService.SERVICE" />
-           </intent-filter>
-        </service>
     </application>
 </manifest>