Introduce a function to return a warning by loggers.

htdocs/core/modules/syslog/logHandlerInterface.php

@@ -48,6 +48,13 @@ interface LogHandlerInterface
 	 */
 	public function getInfo();
 
+	/**
+	 * 	Return warning if something is wrong with logger
+	 *
+	 * 	@return	string		Warning message
+	 */
+	public function getWarning();
+	
 	/**
 	 * 	Return array of configuration data
 	 *