Inconsistent TLD handling

[gavincarr]

Hi Nick,

I think the current (0.19) TLD handling is a bit inconsistent / confusing.

Demo script:

use v5.10;
use Domain::PublicSuffix;

my $dps = Domain::PublicSuffix->new;

say "root:   ", $dps->get_root_domain($ARGV[0]);
say "suffix: ", $dps->suffix;
say "tld:    ", $dps->tld;
say "error:  ", $dps->error;

For a 2LD like "com.au", I get:

./dps com.au
root:
suffix: com.au
tld:    au
error:  Domain is already a suffix

which seems good, but for a TLD, I just get:

./dps com
root:
suffix:
tld:
error:  Malformed domain

which seems wrong ("com" is a valid domain, and a suffix/tld, just not a root domain), and inconsistent e.g. compared with "foo.com":

./dps foo.com
root:   foo.com
suffix: com
tld:    com
error:

Also, we get the same error for unlisted TLDs, which doesn't seem as helpful as the "Invalid TLD" error we get otherwise:

./dps cromulent
root:
suffix:
tld:
error:  Malformed domain

vs.

./dps foo.cromulent
root:
suffix:
tld:
error:  Invalid TLD

Do you think we could do away with the "Malformed domain" error for TLDs?

Thanks,
Gavin