mail/mlmmj: update to 1.6.0
Changes since 1.5.0:
- Lots of portability fixes
- Remove blanks in customheaders prefix and skip empty lines
- $bouncenumbers$ in probe are now expended to number, messageid when possible
- customheaders allow now substitution of $posteraddr$ (Erwan Mas)
- Fix portability issue on Hurd (Erwan Mas)