Add the new 'smart' implementation of Composer's class loader

Composer class loader has changed.
https://github.com/composer/composer/commit/94175ce432e30712fa46ceff1fdee49727542263
It checks the first character of a class, to pre-select prefixes. This is cool!

Adding a "ComposerSmart" class to reflect the changes, and to allow comparison with the old version.