Fixed dynamic loading of Zend View Helpers as Twig Functions

Twig 1.12 broke the ability to dynamically load Zend_View helpers as Twig functions. This patch fixes this (a little dirty tbh)

Ref: https://github.com/fabpot/Twig/commit/44873875ff6ca50c654e3bd28fe19b7ce5108f42
Merge pull request #2 from chrisramakers/master

Fixed dynamic loading of Zend View Helpers as Twig Functions