Add a "smtpname" field on envelopes to remember the server name
advertised during the smtp session that lead to the creation of
an envelope.

Existing on-disk envelopes that don't have that field will have
it set to the default server name on load.
Use the original smtpname as helo and domain when reinjecting a bounce.
Plug a few leaks while there.
Document "show hosts" and "show relays".
Tweak the "show hosts" output while there.
Merge branch 'master' into portable
replace all arc4* calls to csprng_* calls, currently mapped to arc4
csprng
Merge branch 'master' into portable