fixed addExternalMethod

[zmsdev]

Fixed zopeutil.addExternalMethod:
Problem when traversing the hierarchy, Application-Object does not seem to know getParentNode() anymore.
Same fix as in zopeutil.readData()
Could be refactored in a better way.

[drfho]

the try/pass just works around the problem: the Zope- ExtMethod-obj will not be created and thus ZMI shows just an not existing / disfunctional object-ref. In the end this does not work.
The code-area is empty, obvisously: maybe this is the reason why the Zope obj cannot be created (because a function need to referenced in the obj properties). Race-condition?

In ancient times inserting an ExtMethod-attr by default looked like this

[drfho]

#354 (comment)