need to import yafowil.loader

[jensens]

Seems like yafowil.loader is never imported and so the Yafowil factory is empty:

Traceback (innermost last):
  Module ZPublisher.Publish, line 138, in publish
  Module ZPublisher.mapply, line 77, in mapply
  Module ZPublisher.Publish, line 48, in call_object
  Module yafowil.plone.form, line 70, in _call_
  Module yafowil.plone.form, line 56, in render_form
  Module bda.plone.checkout.browser.form, line 337, in prepare
  Module yafowil.base, line 665, in _call_
  Module yafowil.base, line 605, in _expand_blueprints
ValueError: Macro named 'form' is not registered in factory