Add a little more information for unparseable POMs during project dependency-tree discovery.

git-svn-id: https://svn.apache.org/repos/asf/maven/components/trunk@614372 13f79535-47bb-0310-9956-ffa450edef68

maven-project/src/main/java/org/apache/maven/project/artifact/MavenMetadataSource.java

@@ -151,6 +151,10 @@ public class MavenMetadataSource
                             }
                             getLogger().debug( "\n" );
                         }
+                        else
+                        {
+                            getLogger().debug( "", e );
+                        }
                     }
 
                     project = null;