jupyter: erp5_kernel now correctly persists new-style classes without `_p_jar`

If ERP5 Jupyter kernel tried to persist an object created from a new-style class, it would crash because the object has no `_p_jar`. This makes the creation of the ObjectWriter fails. This kind of object needs to be handled by (c)Pickle.

Related to bug report https://nexedi.erp5.net/bug_module/20160819-882FA2, created by @kasra.

@Tyagov, please review when possible. 

/reviewed-on !162

bt5/erp5_data_notebook/ExtensionTemplateItem/portal_components/extension.erp5.JupyterCompile.py

@@ -449,7 +449,7 @@ def canSerialize(obj):
     return all(result_list)
   # if obj is an object and implements __getstate__, ZODB.serialize can check
   # if we can store it
-  elif isinstance(obj, object) and hasattr(obj, '__getstate__'):
+  elif isinstance(obj, object) and hasattr(obj, '__getstate__') and hasattr(obj, '_p_jar'):
     # Need to unwrap the variable, otherwise we get a TypeError, because
     # objects cannot be pickled while inside an acquisition wrapper.
     unwrapped_obj = Acquisition.aq_base(obj)