changed MavenModelMerger extensions visibility to protected to improve

documentation

maven-core/src/main/java/org/apache/maven/model/plugin/DefaultLifecycleBindingsInjector.java

@@ -80,7 +80,7 @@ public class DefaultLifecycleBindingsInjector
         }
     }
 
-    private static class LifecycleBindingsMerger
+    protected static class LifecycleBindingsMerger
         extends MavenModelMerger
     {
 

maven-model-builder/src/main/java/org/apache/maven/model/inheritance/DefaultInheritanceAssembler.java

@@ -124,7 +124,7 @@ public class DefaultInheritanceAssembler
         return adjustment;
     }
 
-    private static class InheritanceModelMerger
+    protected static class InheritanceModelMerger
         extends MavenModelMerger
     {
 

maven-model-builder/src/main/java/org/apache/maven/model/management/DefaultDependencyManagementInjector.java

@@ -50,7 +50,7 @@ public class DefaultDependencyManagementInjector
         merger.mergeManagedDependencies( model );
     }
 
-    private static class ManagementModelMerger
+    protected static class ManagementModelMerger
         extends MavenModelMerger
     {
 

maven-model-builder/src/main/java/org/apache/maven/model/management/DefaultPluginManagementInjector.java

@@ -53,7 +53,7 @@ public class DefaultPluginManagementInjector
         merger.mergeManagedBuildPlugins( model );
     }
 
-    private static class ManagementModelMerger
+    protected static class ManagementModelMerger
         extends MavenModelMerger
     {
 

maven-model-builder/src/main/java/org/apache/maven/model/normalization/DefaultModelNormalizer.java

@@ -93,7 +93,7 @@ public class DefaultModelNormalizer
         }
     }
 
-    private static class DuplicateMerger
+    protected static class DuplicateMerger
         extends MavenModelMerger
     {
 

maven-model-builder/src/main/java/org/apache/maven/model/profile/DefaultProfileInjector.java

@@ -71,7 +71,7 @@ public class DefaultProfileInjector
         }
     }
 
-    private static class ProfileModelMerger
+    protected static class ProfileModelMerger
         extends MavenModelMerger
     {