Add a "stopOnSuccess" JavaBean property to MergingPersonAttributeDaoImpl and CascadingPersonAttributeDaoImpl which would stop the iteration over the child DAOs when some DAO returns without throwing.

This is to extend these DAOs to support the use case of wrapping redundant sources of user attributes present for redundancy -- "try each of these sources in turn, stopping when one of them works, because they are all identical in what they will return for a given query, just existing multiply for redundancy."

If this use case is approved and implemented, this feature should also be added to the standalone PersonAttributeDao project.