[MNG-6114] Elements from the global settings should be ordered before…

… elements from the user settings

This closes apache#142 and closes apache#418

maven-settings-builder/src/main/java/org/apache/maven/settings/merge/MavenSettingsMerger.java

@@ -111,16 +111,19 @@ private static <T extends IdentifiableBase> void shallowMergeById( List<T> domin
                                                                        String recessiveSourceLevel )
     {
         Map<String, T> dominantById = mapById( dominant );
+        final List<T> identifiables = new ArrayList<>( recessive.size() );
 
         for ( T identifiable : recessive )
         {
             if ( !dominantById.containsKey( identifiable.getId() ) )
             {
                 identifiable.setSourceLevel( recessiveSourceLevel );
 
-                dominant.add( identifiable );
+                identifiables.add( identifiable );
             }
         }
+
+        dominant.addAll( 0, identifiables );
     }
 
     /**