File 01-allow-replacing-artifacts.patch of Package maven-jar-plugin

Description: Display a warning instead of failing the build if the plugin
 is misconfigured and attempts to attach twice the same artifact.
Author: Emmanuel Bourg <ebourg@apache.org>
Forwarded: no
Bug: https://issues.apache.org/jira/browse/MJAR-198
--- a/src/main/java/org/apache/maven/plugins/jar/AbstractJarMojo.java
+++ b/src/main/java/org/apache/maven/plugins/jar/AbstractJarMojo.java
@@ -300,7 +300,7 @@
             {
                 if ( projectHasAlreadySetAnArtifact() )
                 {
-                    throw new MojoExecutionException( "You have to use a classifier "
+                    getLog().warn( "You have to use a classifier "
                         + "to attach supplemental artifacts to the project instead of replacing them." );
                 }
                 getProject().getArtifact().setFile( jarFile );