Broker:
- Fix build failure when using WITH_ADNS=yes
- Ensure that an error occurs if `per_listener_settings true` is given after
other security options. Closes #1149.
- Fix include_dir not sorting config files before loading. This was partially
fixed in 1.5 previously.
- Improve documentation around the `include_dir` option. Closes #1154.
- Fix case where old unreferenced msg_store messages were being saved to the
persistence file, bloating its size unnecessarily. Closes #389.
Library:
- Fix `mosquitto_topic_matches_sub()` not returning MOSQ_ERR_INVAL for
invalid subscriptions like `topic/#abc`. This only affects the return value,
not the match/no match result, which was already correct.
Build:
- Don't require C99 compiler.
- Add rewritten build test script and remove some build warnings.