[MNG-4148][MNG-4347] Fixing through-line for the new session-specific metadata source, which is set in the execution request, passed into the session through that, and eventually used in the plugin manager and the extension manager from the session.
maven/maven-2/branches/maven-2.2.x/maven-core/src/main/java/org/apache/maven/execution/DefaultMavenExecutionRequest.java