[COLLECTIONS-508] Clarify javadoc of CollectionBag.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1575586 13f79535-47bb-0310-9956-ffa450edef68
Fix wrong issue number.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1575587 13f79535-47bb-0310-9956-ffa450edef68