add missing release notes

Please include in 6.0.1
(cherry picked from commit ccefa53af3559a7e7492752f1e5255172293d1cb)
Update HISTORY.txt for stepper

Please merge to 6.0.1 release
(cherry picked from commit 870057ab196489ec0019e9bef3b3450a8fe37c9c)
Replaced JPG file with PNG, so future renderer changes don't break test
cases.  Please merge to release branch.
(cherry picked from commit c066040f8d750a16d878b06fc33799bf78a460dc)
update racket HISTORY for v6.0.1