[jdom-interest] wrong error msg

[Jason Hunter]

> Comment and ProcessingInstruction appear to have duplicated code in
> addContent() at least, if there were an interface (terrible names follow) they
> both implemented you could remove the duplicated code, eg:
> 
> interface Addable {
>    String getName(); // "PI" or "Comment" for err msgs
>    Element getParent();
>    Document getDocument();
> }

Then I could make my Widget class implement Addable and have Widgets
hanging all over my document.  That's the problem with using typed
interfaces to enforce rules, it lets you create non-well-formed XML.

-jh-