[COLLECTIONS-533] Initial commit for MultiValuedLinkedHashMap implementation & tests. Thanks to Geoff Schoeman.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1632534 13f79535-47bb-0310-9956-ffa450edef68
[COLLECTIONS-533] Changing SetValuedLinkedHashMap's default collection to LinkedHashSet to preserve insertion order & some more tests

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1632539 13f79535-47bb-0310-9956-ffa450edef68