Avoid using Twig_Environment::getFunction to identify Assetic functions
Avoid using Twig_Environment::getFunction to identify Assetic functions

As of Assetic 1.3.0, the Twig functions are using a special node class,
which can be used to identify them instead.

kriswallsmith/assetic,kriswallsmith/assetic,kriswallsmith/assetic,kriswallsmith/assetic