revert to the first implementation concept:

trusted adapters provide always a location.

untrusted adapters provide a location unless
its factories are public.

if an adapter does not provide ILocation itself
it gets location-proxied. such an adapter is
not directly pickable because location proxies
are not pickable. if you use pickalbe adapters
they should provide ILocation.

adapter.py

@@ -238,6 +238,8 @@ def assertLocation(adapter, parent):
         return adapter
 
 
+# BBB: The trusted adapter factory is replaced by the locating trusted adapter
+# factory
 class TrustedAdapterFactory(TrustedAdapterFactoryMixin):
     """Adapt an adapter factory to to provide trusted adapters