checkstyle: proper multiple empty line check

Hopefully checkstyle could catch all of these on its own one day. For
now, help it via a multiline regex.

F-Droid/src/com/google/zxing/integration/android/IntentIntegrator.java

@@ -400,7 +400,6 @@ public class IntentIntegrator {
         return downloadDialog.show();
     }
 
-
     /**
      * <p>Call this from your {@link Activity}'s
      * {@link Activity#onActivityResult(int, int, Intent)} method.</p>
@@ -432,7 +431,6 @@ public class IntentIntegrator {
         return null;
     }
 
-
     /**
      * Defaults to type "TEXT_TYPE".
      *

F-Droid/src/org/fdroid/fdroid/AppDetails.java

@@ -1205,7 +1205,6 @@ public class AppDetails extends AppCompatActivity implements ProgressListener, A
             final TextView summaryView = (TextView) view.findViewById(R.id.summary);
             summaryView.setText(app.summary);
 
-
             layoutLinks = (ViewGroup) view.findViewById(R.id.ll_information);
             layoutLinksContent = (ViewGroup) layoutLinks.findViewById(R.id.ll_information_content);
 

F-Droid/src/org/fdroid/fdroid/localrepo/SwapService.java

@@ -116,7 +116,6 @@ public class SwapService extends Service {
         bluetoothFinder.cancel();
     }
 
-
     // ==========================================================
     //                 Manage the current step
     // ("Step" refers to the current view being shown in the UI)
@@ -287,7 +286,6 @@ public class SwapService extends Service {
     @Retention(RetentionPolicy.SOURCE)
     public @interface SwapStep { }
 
-
     // =================================================
     //    Have selected a specific peer to swap with
     //  (Rather than showing a generic QR code to scan)
@@ -312,7 +310,6 @@ public class SwapService extends Service {
         return peer;
     }
 
-
     // ==========================================
     //      Remember apps user wants to swap
     // ==========================================
@@ -373,7 +370,6 @@ public class SwapService extends Service {
         persistAppsToSwap();
     }
 
-
     // =============================================================
     //   Remember which swap technologies a user used in the past
     // =============================================================
@@ -469,7 +465,6 @@ public class SwapService extends Service {
     public static final String ACTION_PEER_FOUND = "org.fdroid.fdroid.SwapManager.ACTION_PEER_FOUND";
     public static final String EXTRA_PEER = "EXTRA_PEER";
 
-
     // ===============================================================
     //        Old SwapService stuff being merged into that.
     // ===============================================================

F-Droid/src/org/fdroid/fdroid/localrepo/type/BluetoothSwap.java

@@ -44,8 +44,6 @@ public final class BluetoothSwap extends SwapType {
     private BluetoothSwap(@NonNull Context context, @NonNull BluetoothAdapter adapter) {
         super(context);
         this.adapter = adapter;
-
-
     }
 
     @Override

F-Droid/src/org/fdroid/fdroid/net/AsyncDownloaderFromAndroid.java

@@ -341,7 +341,6 @@ public class AsyncDownloaderFromAndroid implements AsyncDownloader {
         return -1;
     }
 
-
     /**
      * Check if download was valid, see issue
      * http://code.google.com/p/android/issues/detail?id=18462

F-Droid/src/org/fdroid/fdroid/net/bluetooth/BluetoothClient.java

@@ -23,7 +23,6 @@ public class BluetoothClient {
 
     public BluetoothConnection openConnection() throws IOException {
 
-
         BluetoothSocket socket = null;
         BluetoothConnection connection = null;
         try {

F-Droid/src/org/fdroid/fdroid/net/bluetooth/BluetoothServer.java

@@ -358,5 +358,4 @@ public class BluetoothServer extends Thread {
         }
     }
 
-
 }

F-Droid/src/org/fdroid/fdroid/views/fragments/PreferencesFragment.java

@@ -320,5 +320,4 @@ public class PreferencesFragment extends PreferenceFragment
         updateSummary(key, true);
     }
 
-
 }

F-Droid/test/src/android/test/ProviderTestCase2MockContext.java

@@ -168,7 +168,6 @@ public abstract class ProviderTestCase2MockContext<T extends ContentProvider> ex
         }
     }
 
-
     /**
      * Gets the {@link MockContentResolver} created by this class during initialization. You
      * must use the methods of this resolver to access the provider under test.

F-Droid/test/src/org/fdroid/fdroid/TestUtils.java

@@ -222,7 +222,6 @@ public class TestUtils {
         Context context = instrumentation.getContext();
         Context targetContext = instrumentation.getTargetContext();
 
-
         File[] dirsToTry = new File[]{
             context.getCacheDir(),
             context.getFilesDir(),

F-Droid/test/src/org/fdroid/fdroid/compat/FileCompatForTest.java

@@ -24,5 +24,4 @@ public class FileCompatForTest extends FileCompat {
         symlinkLibcore(source, dest);
     }
 
-
 }

config/checkstyle/checkstyle.xml

@@ -14,6 +14,14 @@
         <property name="severity" value="info" />
     </module>
 
+    <module name="RegexpMultiline">
+        <property name="format" value="\n\n\n" />
+        <property name="minimum" value="0" />
+        <property name="maximum" value="0" />
+        <property name="message" value="Multiple empty lines found." />
+        <property name="severity" value="info" />
+    </module>
+
     <module name="TreeWalker">
 
         <!--<module name="ConstantName" />-->