Hint 2: jcrName is currently required for field mapping

[Dan Connelly]

DTD says jcrName in field descriptors is implied.   When not given, the 
fieldName should be taken as the jcrName.

In fact, the Node name string will be left as null in the current 
code.    This cause will cause NPEs in Jackrabbit.

Must give jcrName explicitly for every field in the jcr mapping file.

      -- Dan