[UIMA-4061] PositiveIntSet enhancement, use for FSBagIndex.

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1636458 13f79535-47bb-0310-9956-ffa450edef68
[UIMA-4083] fixes for JSON serialization

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1636459 13f79535-47bb-0310-9956-ffa450edef68
[UIMA-4083] fixes for JSON serialization, new tests

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1636460 13f79535-47bb-0310-9956-ffa450edef68