Avoid possible recursion in log statement within AuditableInterceptor

Actually, when running reporting tests against 1.7+ we are facing to stackoverflow error because of this line in AuditableInterceptor:

log.debug("Setting changed by fields on " + entity);

Actually, invoking entity.toString() makes recursive call of this interceptor.
Fix it in this way:

log.debug("Setting changed by fields on " + entity.getClass());