Dexterity 2.0 makes zope.app.content only a soft-dependency (details). Add-ons that want it must declare a dependency on it in their install_requires.
Sorry I should make it clearer that if you have an answer please post it on stack overflow because the poster may not be reading this thread here
Yeah, did that first. Just linking back to the answer in my reply, as I'm a messy eater, dropping breadcrumbs everywhere... 
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