Added a class PEP252Mixin. By adding this to your ObjectDefinition you
get PEP-252 style objects in stead of old-fashioned objects.
In stead of defining a GetattrHook you declare a class variable getsetlist,
which contains tuples (name, getcode, setcode, docstring).
Only lightly tested: the code still works if you don't inherit PEP252Mixin
and the code works if you inherit it but don't define any getters
or setters. Also, this will not work together with the "poor mans inheritance"
offered by method chains, so the CF module will remain with old-style
objects until PEP253 is supported too.