Solution 

• Version 2

#!/usr/bin/perl -nl
($a, $b) = split /\./;
$h{"$a.$b"} = 1;
$h{"$a.M"} = 1;
END { print join("\n", sort keys %h); }

• perl -l - enable line ending processing, specifies line terminator

• but without specifying the terminator...

• ...acts like chomp on each line

• first hack!