Made the first registration-related tests pass. See the TXT files in

zope.app.component.

Along the way I noticed that there are many circular imports in all of 
this code. I think that my refactorings will improve the situation.

zopepublication.py

@@ -49,7 +49,7 @@
 from zope.app.security.principalregistry import principalRegistry as prin_reg
 from zope.app.security.interfaces import IUnauthenticatedPrincipal
 from zope.app.security.interfaces import IAuthenticationUtility
-from zope.app.site.interfaces import ISite
+from zope.app.component.interfaces import ISite
 from zope.app.traversing.interfaces import IPhysicallyLocatable
 
 class Cleanup(object):