Handle prepended autoloader
bug #108 Check for composer autoloader (goetas)

This PR was merged into the 2.3.x-dev branch.

Discussion
----------

Check for composer autoloader

Is not always true that first autoloader is a composer autoloader.
using `spl_autoload_register` with `$prepend = true` will produce errors as:

*Fatal error: Cannot use object of type Closure as array in vendor/sensio/distribution-bundle/Sensio/Bundle/DistributionBundle/Composer/ScriptHandler.php on line 161*
or similar

Commits
-------

ad4fb3e Handle prepended autoloader