map2postfix-transport.rb: generic .onion and records for local site

[taggart]

A couple things I thought of about the output of map2postfix-transport.rb:

• it does not output a generic onion entry .onion smtptor:. We had used this in the past to cover any MX records that pointed to onion addresses directly. I don't know if this is common at all, or if it should be encouraged/discouraged
• for records in the map that are your own organization, you might not want them in there to avoid the extra transport via tor for what is probably already going over loopback (or maybe a private network to another host). When generating this map I always pruned these by hand just to be safe. Ideally in your transports you'd have some sort of local transport map listed first before the SRV lookup and this static map so these records shouldn't matter. But it does still seem like a potential pitfall for people setting this up. Options: 1) document the pitfall(not great) 2) make the script filter local domains(janky) 3) stop doing a static map and only do SRV(solves static map but not the same pitfall in SRV).

Opinions?