[packages/postgrey] - migrate configuration to /etc/postfix

[Marcin Krol]

> In ALT, we've moved exactly towards multiple versions so that
> people switch (and dump/restore) between them when they know it,
> and not after an overlooked line in dist-upgrade's output...
> (when it's too late to use the upgraded "dumper" for that)

With multiple versions installed it is easier to switch using pg_upgrade 
rather than dump/restore not to mention that running several versions at 
once gives way more flexibility for both admins and software developers.

M.