Documentation and code ignores the fact that __getattr__ always works on acquisition unwrapped objects

[do3cc]

This causes surprising and bad behavior:

1. Create a schema
2. Add a IContextAwareDefaultFactory for one of the fields. The factory should try to access the parent
3. A view will show the information from the parent
4. Accessing the property directly in code will fail. The object is acquisition wrapped, but Python doesn't know about this magic and __getattr__ gets an unwrapped object of self. All __parent__ pointers are gone.

I wouldn't know how to fix it, unfortunately. And it should be added somewhere as a warning.

[do3cc]

For more context: http://stackoverflow.com/questions/35799092/how-to-test-a-content-type-with-a-icontextawaredefaultfactory

[do3cc]

@jensens @saily thinks, you know what to do here