[Debug] ensured that the Debug tools can only be registered once

src/Symfony/Component/Debug/Debug.php

@@ -20,8 +20,26 @@ use Symfony\Component\ClassLoader\DebugClassLoader;
  */
 class Debug
 {
+    private static $enabled = false;
+
+    /**
+     * Enables the debug tools.
+     *
+     * This method registers an error handler and an exception handler.
+     *
+     * If the Symfony ClassLoader component is available, a special
+     * class loader is also registered.
+     *
+     * @param integer $errorReportingLevel The level of error reporting you wan
+     */
     public static function enable($errorReportingLevel = null)
     {
+        if (static::$enabled) {
+            return;
+        }
+
+        static::$enabled = true;
+
         error_reporting(-1);
         ini_set('display_errors', 0);
 

src/Symfony/Component/Debug/ErrorHandler.php

@@ -47,7 +47,7 @@ class ErrorHandler
     private static $logger;
 
     /**
-     * Register the error handler.
+     * Registers the error handler.
      *
      * @param integer $level The level at which the conversion to Exception is done (null to use the error_reporting() value and 0 to disable)
      *

src/Symfony/Component/Debug/ExceptionHandler.php

@@ -41,7 +41,7 @@ class ExceptionHandler
     }
 
     /**
-     * Register the exception handler.
+     * Registers the exception handler.
      *
      * @param Boolean $debug
      *