minor #2649 Make a small performance improvement (fabpot)

This PR was merged into the 2.x branch.

Discussion
----------

Make a small performance improvement

And it also fixes some potential subtle bugs.

Commits
-------

27f905ed made a small performance improvement

lib/Twig/ExtensionSet.php

@@ -160,6 +160,8 @@ final class Twig_ExtensionSet
             throw new LogicException(sprintf('Unable to register extension "%s" as it is already registered.', $class));
         }
 
+        // For BC/FC with namespaced aliases
+        $class = (new ReflectionClass($class))->name;
         $this->extensions[$class] = $extension;
     }
 

lib/Twig/Template.php

@@ -41,11 +41,7 @@ abstract class Twig_Template
     public function __construct(Twig_Environment $env)
     {
         $this->env = $env;
-        foreach ($env->getExtensions() as $extension) {
-            // For BC/FC with namespaced aliases
-            $class = (new ReflectionClass(get_class($extension)))->name;
-            $this->extensions[ltrim($class, '\\')] = $extension;
-        }
+        $this->extensions = $env->getExtensions();
     }
 
     /**