Send the total number of iterations with the ENCRYPT and DECRYPT

Send the total number of iterations with the ENCRYPT and DECRYPT
status messages. This can make it easier for a client to do use things
like progress bars when the number of iterations differs from the
configuration value (no file is open yet, and the file header contains
the actual number of iterations).

Also set the "iterations" configuration parameter after a successful
OPEN. This will keep the iteration setting for the next SAVE. To
change it, use OPTION ITERATIONS. The original configuration value is
now only used for new files.