Another bugfix: sometimes, very early during execution, a class with...

Another bugfix: sometimes, very early during execution, a class with namespaces might not be autoloaded yet, and if we are asked to load the old class without namespaces, it will fail. Make it load the file corresponding to the class first, and see if it exists then. If not, try to see if it has been migrated to namespaces, and create the alias then.