SEVERE error messages for other plugins, that try to manually enable Essentials, FakePermissions or GroupManager

EssentialsGroupManager/src/org/anjocaido/groupmanager/GroupManager.java

@@ -63,6 +63,10 @@ public class GroupManager extends JavaPlugin {
 
     @Override
     public void onEnable() {
+		if (!Thread.currentThread().getStackTrace()[5].getMethodName().equals("loadPlugin")) {
+			logger.log(Level.SEVERE, "Another plugin is trying to enable Essentials manually. Don't do this! It's probably "
+					+ Thread.currentThread().getStackTrace()[5].getClassName());
+		}
         GroupManager.logger.setUseParentHandlers(false);
         GMLoggerHandler ch = new GMLoggerHandler();
         GroupManager.logger.addHandler(ch);