[jdom-interest] getMixedContent -> getContent

[philip.nelson at omniresources.com]

> Considering we have addContent() and removeContent() it seems to make
> simple sense to have getContent() and setContent().  So 
> that's the easy
> one to tackle.  The other changes involve debate.

+1 on getContent() rename

lot's o' code changes here.  If we ever change this again, I may use
frequent flyer miles to come out there and ......