add warning if artifact with sources classifier not found

git-svn-id: https://svn.apache.org/repos/asf/maven/plugin-tools/branches/MPLUGIN-189@1336293 13f79535-47bb-0310-9956-ffa450edef68

maven-plugin-tools-annotations/src/main/java/org/apache/maven/tools/plugin/annotations/JavaAnnotationsMojoDescriptorExtractor.java

@@ -212,6 +212,9 @@ public class JavaAnnotationsMojoDescriptorExtractor
         {
             //throw new ExtractionException( e.getMessage(), e );
             getLogger().debug( "skip ArtifactNotFoundException:" + e.getMessage() );
+            getLogger().warn(
+                "Impossible to get sources artifact for " + artifact.getGroupId() + ":" + artifact.getArtifactId() + ":"
+                    + artifact.getVersion() + ". Some javadoc tags (@since, @deprecated and comments) won't be used" );
         }
         catch ( NoSuchArchiverException e )
         {