Resolve #97 and keep #98 safe

pf4j/src/main/java/ro/fortsoft/pf4j/AbstractExtensionFinder.java

@@ -85,16 +85,13 @@ public abstract class AbstractExtensionFinder implements ExtensionFinder, Plugin
                         extensionWrapper.setExtensionFactory(pluginManager.getExtensionFactory());
                         result.add(extensionWrapper);
                         log.debug("Added extension '{}' with ordinal {}", className, ordinal);
-                    } else {
-                        // it's too verbose the below block (uncomment if you are in trouble)
-                        /*
-                        log.warn("'{}' is not an extension for extension point '{}'", className, type.getName());
-                        ClassLoader classLoader1 = type.getClassLoader();
-                        ClassLoader classLoader2 = extensionClass.getClassLoader();
-                        if (!classLoader1.equals(classLoader2)) {
-                            log.warn("Different class loaders: '{}' and '{}'", classLoader1, classLoader2);
+                    } else if (log.isTraceEnabled()) { // an alternative may be the use of a system property
+                        log.trace("'{}' is not an extension for extension point '{}'", className, type.getName());
+                        ClassLoader typeClassLoader = type.getClassLoader();
+                        ClassLoader extensionClassLoader = extensionClass.getClassLoader();
+                        if (!typeClassLoader.equals(extensionClassLoader)) {
+                            log.trace("Different class loaders: '{}' and '{}'", typeClassLoader, extensionClassLoader);
                         }
-                        */
                     }
                 } catch (ClassNotFoundException e) {
                     log.error(e.getMessage(), e);