Add local hostname to $mydestination

This should allow mails sent from localhost to <account>@<hostname> to
be delivered, remote mails still need to have FQDN recipient.
Support case where FQDN domain is not defined

In case a FQDN is not defined, Postfix will try and do it's best sending
all mail to its hostname; Postfix capabilities are automatically
overriden to enable local mail delivery.
Remove fix for problems with localhost/IP address

Looks like old errors on connections from [::1] aren't showing up
anymore in logs, so this fix shouldn't be needed anymore.
Merge pull request #8 from drybjed/postfix-fixes

Postfix fixes and small modifications