v4.30

• follow-up to b36f925 - add back handling of attachment content name
• fixes #142 - improved message list attachment indication
• fixes #141 - fix character set conversion issue causing truncated output
• default to release build without debug info for git clones
• remove nspell-gpt as default spell checker
• fixes #96 - smtp handshake to send ip instead of hostname by default
• integrate dinhvh/libetpan#433 - fix mailsmtp_init_with_ip for IPv6 on Linux
• add libetpan to source tree - based on dinhvh/libetpan@5c9eb6b