net_utils: added get_public_ip, using 'stun' package
qmd: when relaying, validate MAIL FROM against QMD

and refactored the code a little, to avoid redundancy
qmd: added config:check_outbound option
qmd: move the callback to the last argument

to get_qmd_response
Merge pull request #534 from msimerson/qmd

qmd: when relaying, validate MAIL FROM against QMD
Merge pull request #536 from msimerson/net_utils

net_utils: added get_public_ip, using 'stun' package
spf: SPF results were invalid if TXT record exceeded 25? bytes.

this appends additional TXT strings to the record (completing it)