Then I wrote a quick script to do the table lookup ..

#!/usr/bin/perl -w

#  Which distribution do these modules come from?
#
#  Arguments:
#    Text file containing data from CPAN
#    List of modules

{
    my ( $cpanList, $localList ) = @ARGV;
    my %list;


    #  Load up the CPAN information.

    open ( CPAN, $cpanList ) or
      die "Unable to open $cpanList: $!";

    #  Skip the file header.

    while(<CPAN>) {
      next if ( /^\S+:\s+/ );
      next if ( /^\s*$/ );
      last;
    }

    # Load data into a Hash for later retrieval.

    while(<CPAN>) {
      my ( $module, undef, $distro ) = split(' ',$_);
      $distro =~ s#^.+/##;

      $list{$module} = $distro;
    }

    close ( CPAN );

    #  Look through the list of the modules, outputting which distro 
    #  contains that module.

    open ( LIST, $localList ) or
      die "Unable to open $localList: $!";

    while (<LIST>) {
      chomp;
      if ( defined($list{$_} ) ) {
        printf ( "%30s comes from %s\n", $_, $list{$_} );
      } else {
        print "Not able to find out where $_ came from.\n";
      }
    }

    close ( LIST );
}
[download]

The code works, and it discovered two internal Perl modules that I'd left in, as well as a few Apache sub-modules. The next step is to re-factor that code so that we group together things that came from the same distribution, but that's a refinement that I'll leave till later. Anyway, that answers my original question.

Update: You can find out about the Apache modules here on the mod_perl web site.