Include Products.CMFCore package in browser/configure.zcml, per
http://plone.org/documentation/manual/upgrade-guide/version/upgrading-plone-4.0-to-4.1/updating-add-on-products-for-plone-4.1/changing-dependencies-from-plone-to-products.cmfplone
for Plone 4.1+ compatibility.

Fixes Issue #7.