Made sure drop_type__cascade_p parameter has a meaning which is to drop all the objects of a certain type when dropping the object_tpye. Note that this does not work for content_types. Use the according procedure there. Not written in Oracle as there might be a reason for not using the __cascade_p parameter and then I don't want to have done the work of porting to Oracle for nothing
Made sure that you can actually delete xowiki comletely from your system. Albeit this only works with OpenACS 5.3, but I am not to introduce a dependency on this and the uninstalling of the package did not work before, so no harm done :)