Allow self-registration to work outside Composer too
Summary:
Unit test for self-registration only checked we add an autoloader
function, but didn't test the correctness of the autoloader.
The autoloader worked fine if an autoloader is already there,
but if not will complain about missing classes.
Test Plan: Tested without vendor/ folder
Reviewers: dereckson
Reviewed By: dereckson
Differential Revision: https://devcentral.nasqueron.org/D2546