Hint 3: jcrNodeType is required when interface="true"

[Dan Connelly]

Same story (roughly) as in Hint 2.    jcrNodeType is left null for 
interfaces if it is not stated explicitly in the mapping file.

This is (almost) forgiveable in this case since the stated default node 
tyep, nt.unstructured, does not work for interfaces.

As a workaround, I give the jcrNodeType explicity as "graffito:content" 
in class descriptors where interface="true".

      -- Dan