Pull in a couple of interop and memory leak fixes
    
    - pull in fix from master to return a NULL pointer rather than allocating
      zero bytes of memory if we read a zero-length input token (RT#7794, part
      of #1043962)
    - pull in fix from master to ignore an empty token from an acceptor if
      we've already finished authenticating (RT#7797, part of #1043962)
    - pull in fix from master to avoid a memory leak when a mechanism's
      init_sec_context function fails (RT#7803, part of #1043962)
    - pull in fix from master to avoid a memory leak in a couple of error
      cases which could occur while obtaining acceptor credentials (RT#7805,
      part of #1043962)