make ClassLoaderLeakPreventorFactory configurable and mark BootstrapClassLoader as shutdown

scm-webapp/src/main/java/sonia/scm/lifecycle/classloading/BootstrapClassLoader.java

@@ -5,7 +5,29 @@ package sonia.scm.lifecycle.classloading;
  * find it in a heap dump.
  */
 class BootstrapClassLoader extends ClassLoader {
+
+  /**
+   * Marker to find a BootstrapClassLoader, which is already shutdown.
+   */
+  private boolean shutdown = false;
+
   BootstrapClassLoader(ClassLoader webappClassLoader) {
     super(webappClassLoader);
   }
+
+  /**
+   * Returns {@code true} if the classloader was shutdown.
+   *
+   * @return {@code true} if the classloader was shutdown
+   */
+  boolean isShutdown() {
+    return shutdown;
+  }
+
+  /**
+   * Mark the class loader as shutdown.
+   */
+  void markAsShutdown() {
+    shutdown = true;
+  }
 }