Fix - Call to undefined function Composer\Autoload\includeFile()

[johanjanssens]

Joomla 3.4 is extending Composer\Autoload\ClassLoader to make sure JLoader::applyAliasFor($class); is called when a class is being loaded.

Description

The implementation in Joomla 3.4 prevents to use composer in your own extension and requires developers to implement a workaround first.

To resolve this the PR rewrites the implementation and instead of extending Composer\Autoload\ClassLoader it decorates it. This is the advised approach to handle this scenario by the Composer team. For details see following discussion.

Additionally the fix brings the Composer integration in Joomla more inline with Composer itself. The specialised composer_autoload.php file is removed in favour of the autoload.php file generated by Composer.

List of changes

• Remove /libraries/composer_autoload.php use default /libraries/vendor/autoload.php as per composer specification
• Decorate \Composer\Autoload\ClassLoader through JClassLoader
• Unregister default class loader and register decorator during Joomla Cms bootstrapping

Testing instructions

Make sure Joomla still works.

[johanjanssens]

Pull Request joomla#6335