Allow multiple resource bundles for a given locale to be managed by same DefaultMessageResources instance.
This is useful in a use case scenario of modularly developed webapps, to allow the resources to be updated for each module.
The MessageResources#useResource() should more properly become a #useURI() and the URI string will be interpreted accordingly by each impl. Eg, by the default bundle-based impl, the URI can simply be a CSV-list of bundle names.
Moreover, one could envisage a db-based impl, where the URI is the connection string.