Resolving: MNG-800...needed a call to flush the cached plugins-by-key map in the registry when a new plugin is added.

git-svn-id: https://svn.apache.org/repos/asf/maven/components/trunk@292222 13f79535-47bb-0310-9956-ffa450edef68

maven-core/src/main/java/org/apache/maven/plugin/version/DefaultPluginVersionManager.java

@@ -561,6 +561,8 @@ public class DefaultPluginVersionManager
             plugin.setUseVersion( version );
 
             pluginRegistry.addPlugin( plugin );
+            
+            pluginRegistry.flushPluginsByKey();
         }
 
         writeUserRegistry( groupId, artifactId, pluginRegistry );