Fix anonymous class serialization warnings

Anonymous inner classes are replaced by a dedicated comparator class.

NOTE: Also introducing classes to keep XStream backward compatibility.
This was missed in the previous attempt in commit 2366eae.

The warnings from org.jenkinsci.remoting.util.AnonymousClassWarnings have been:
> "Attempt to (de-)serialize anonymous class org.jenkinsci.plugins.configfiles.GlobalConfigFiles$1 ..."
> "Attempt to (de-)serialize anonymous class org.jenkinsci.plugins.configfiles.folder.FolderConfigFileProperty$1 ..."
see: https://wiki.jenkins.io/display/JENKINS/Serialization+of+anonymous+classes

src/main/java/org/jenkinsci/plugins/configfiles/ConfigByIdComparator.java

@@ -0,0 +1,14 @@
+package org.jenkinsci.plugins.configfiles;
+
+import org.jenkinsci.lib.configprovider.model.Config;
+
+import java.io.Serializable;
+import java.util.Comparator;
+
+public class ConfigByIdComparator implements Comparator<Config>, Serializable {
+
+    @Override
+    public int compare(Config c1, Config c2) {
+        return c1.id.compareTo(c2.id);
+    }
+}

src/main/java/org/jenkinsci/plugins/configfiles/GlobalConfigFiles$1.java

@@ -0,0 +1,18 @@
+package org.jenkinsci.plugins.configfiles;
+
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.DoNotUse;
+
+/**
+ * This class is required for XStream backward compatibility because {@link GlobalConfigFiles}
+ * formerly contained an anonymous inner class defining the comparator.
+ *
+ * For old XML configurations that still contain a comparator element as follows
+ * {@code <comparator class="org.jenkinsci.plugins.configfiles.GlobalConfigFiles$1"/>}
+ * XStream tries to resolve a class named exactly like this during deserialization.
+ *
+ * @deprecated replaced by {@link ConfigByIdComparator}
+ */
+@Deprecated
+@Restricted(DoNotUse.class)
+final class GlobalConfigFiles$1 extends ConfigByIdComparator {}

src/main/java/org/jenkinsci/plugins/configfiles/GlobalConfigFiles.java

@@ -30,12 +30,7 @@
 @Symbol("globalConfigFiles")
 public class GlobalConfigFiles extends GlobalConfiguration implements ConfigFileStore {
 
-    private static Comparator<Config> COMPARATOR = new Comparator<Config>() {
-        @Override
-        public int compare(Config o1, Config o2) {
-            return o1.id.compareTo(o2.id);
-        }
-    };
+    private static Comparator<Config> COMPARATOR = new ConfigByIdComparator();
 
     private static ConfigProviderComparator CONFIGPROVIDER_COMPARATOR = new ConfigProviderComparator();
 

src/main/java/org/jenkinsci/plugins/configfiles/folder/FolderConfigFileProperty$1.java

@@ -0,0 +1,19 @@
+package org.jenkinsci.plugins.configfiles.folder;
+
+import org.jenkinsci.plugins.configfiles.ConfigByIdComparator;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.DoNotUse;
+
+/**
+ * This class is required for XStream backward compatibility because {@link FolderConfigFileProperty}
+ * formerly contained an anonymous inner class defining the comparator.
+ *
+ * For old XML configurations that still contain a comparator element as follows
+ * {@code <comparator class="org.jenkinsci.plugins.configfiles.folder.FolderConfigFileProperty$1"/>}
+ * XStream tries to resolve a class named exactly like this during deserialization.
+ *
+ * @deprecated replaced by {@link ConfigByIdComparator}
+ */
+@Deprecated
+@Restricted(DoNotUse.class)
+final class FolderConfigFileProperty$1 extends ConfigByIdComparator {}

src/main/java/org/jenkinsci/plugins/configfiles/folder/FolderConfigFileProperty.java

@@ -8,6 +8,7 @@
 import net.sf.json.JSONObject;
 import org.jenkinsci.lib.configprovider.ConfigProvider;
 import org.jenkinsci.lib.configprovider.model.Config;
+import org.jenkinsci.plugins.configfiles.ConfigByIdComparator;
 import org.jenkinsci.plugins.configfiles.ConfigByNameComparator;
 import org.jenkinsci.plugins.configfiles.ConfigFileStore;
 import org.jenkinsci.plugins.configfiles.ConfigProviderComparator;
@@ -16,15 +17,9 @@
 import java.io.IOException;
 import java.util.*;
 
-
 public class FolderConfigFileProperty extends AbstractFolderProperty<AbstractFolder<?>> implements ConfigFileStore {
 
-    private static Comparator<Config> COMPARATOR = new Comparator<Config>() {
-        @Override
-        public int compare(Config o1, Config o2) {
-            return o1.id.compareTo(o2.id);
-        }
-    };
+    private static Comparator<Config> COMPARATOR = new ConfigByIdComparator();
 
     private static ConfigProviderComparator CONFIGPROVIDER_COMPARATOR = new ConfigProviderComparator();