add groupId org.apache.maven.plugins for official Apache Maven plugins

We know that :   Calling it maven-< yourplugin >-plugin (note "Maven" is at the beginning of the plugin name) is strongly discouraged since it's a reserved naming pattern for official Apache Maven plugins maintained by the Apache Maven team with groupId org.apache.maven.plugins. Using this naming pattern is an infringement of the Apache Maven Trademark.   from http://maven.apache.org/guides/plugin/guide-java-plugin-development.html#Plugin_Naming_Convention_and_Apache_Maven_Trademark , but some plugins  may not keep this standard. 

For Example: maven-replacer-plugin(version 1.4.1) in pom belongs  < groupId >com.google.code.maven-replacer-plugin< /groupId >, though its artifactId was renamed to "replacer" from "maven-replacer-plugin" due to a naming policy change from the Maven team since version 1.5.0. Pls see http://code.google.com/p/maven-replacer-plugin/ 

If we add < groupId >org.apache.maven.plugins< /groupId > for official Apache Maven plugins, there will be no ambiguity.