JSON serialization in uima core wrong context, sometimes

Running json test in v3 revealed two bugs in the JSON serialization.
1) reset the cache in "sortedUsedTypes" when starting serailization because this may have changed (in CasSerializerSupport)
2) Also in CasSerializerSupport - make the static Comparator used for sorting types used, public, so it can be used by the JSON serializer code when doing a binary search to see if a type is present.
3) Change the code in JsonCasSerializer which does the binary search to use this same comparator, because the search must use the same sort ordering.