Now that `define` and `require` are never made public, we have to
build everything to support `$.fn.select2.amd` while also working
with other AMD loaders.
This will prevent leaking variables, and will remove the possibility
of Select2 not working well with other plugins which support
AMD loaders. The `define` and `require` methods are now aliased
under `$.Select2.amd` for use inside additional files, such as
translations.