Update the MCDO0551 READMEs again.

Mention Robert Hall's Minix port; give more information
about McDonald's and Picton's versions as far as I'm aware.

The significance of the combination to Long's safe (7-22-34)
is that it's the date of John Dillinger's death. Picton
changes it to be different in every game, and also changes
some magic words (such as PHUCE) so that they won't work
until you've "properly" discovered them.