Added SortedSet and test cases
Add Set comment
Add OidSet comment
Fix SortedSet.clone(), intersection() result incorrect type
Merge branch 'sortedset'
Add Set.clone(), union(), intersection(), difference() result type check test cases
Modify type check test cases from "test.isTrue()" to "test.instanceOf()"
Merge branch 'master' into oidset
Change "OidSet.elements[]" sets from "Set" to "SortedSet"
Add OidSet.clone(), union(), intersection(), difference() result type check test cases
Change OidSet.remove(), contains() and test cases from "Set" to "SortedSet"