* ZNAK's do not include a file position (according to ZMODEM.DOC).
* ZRINIT's received between files are now parsed for options.
* When finishing a session by sending ZFIN and no ZFIN is received in response,
  up to 10 (by default) ZABORTs and ZFINs are sent alternately.
* If a ZRPOS is received in response to a sent ZEOF, continue the transfer.
* If first file in batch is unsuccessfully sent, stop the batch.