Shorten all variable names

(102 strokes) Of course, up to now, we've been shooting for readable code.

#!perl -pl
sub p {
	$D || print "$P.M";
}
/$P/ or$D=!p;
/\./;
$P=$`;
$D=/M$/ || p if /[M-Z]$/;
END {
	$.&&p
}