This is a bugfix release.

Packaging changes

The snap package now has support for websockets included.
The Windows packages have changed.
- Support for Windows XP was dropped in Mosquitto 1.5, so the need for the Cygwin build has gone, and this has been dropped.
- There are now 64-bit and 32-bit native packages.
- Websockets support is included.
- Threading support is not included in libmosquitto to simplify installation, alternative solutions are being looked into for the future.
- The only external dependency is now OpenSSL.

Version 1.5.1 changes

Broker

Fix plugin cleanup function not being called on exit of the broker. Closes #900.
Print more OpenSSL errors when loading certificates/keys fail.
Use AF_UNSPEC etc. instead of PF_UNSPEC to comply with POSIX. Closes #863.
Remove use of AI_ADDRCONFIG, which means the broker can be used on systems where only the loopback interface is defined. Closes #869, Closes #901.
Fix IPv6 addresses not being able to be used as bridge addresses. Closes #886.
All clients now time out if they exceed their keepalive*1.5, rather than just reach it. This was inconsistent in two places.
Fix segfault on startup if bridge CA certificates could not be read. Closes #851.
Fix problem opening listeners on Pi caused by unsigned char being default. Found via #849.
ACL patterns that do not contain either %c or %u now produce a warning in the log. Closes #209.
Fix bridge publishing failing when per_listener_settings was true. Closes #860.
Fix use_identity_as_username true not working. Closes #833.
Fix UNSUBACK messages not being logged. Closes #903.
Fix possible endian issue when reading the memory_limit option.
Fix building for libwebsockets < 1.6.
Fix accessor functions for username and client id when used in plugin auth check.

Library

Fix some places where return codes were incorrect, including to the on_disconnect() callback. This has resulted in two new error codes, MOSQ_ERR_KEEPALIVE and MOSQ_ERR_LOOKUP.
Fix connection problems when mosquitto_loop_start() was called before mosquitto_connect_async(). Closes #848.

Clients

When compiled using WITH_TLS=no, the default port was incorrectly being set to -1. This has been fixed.
Fix compiling on Mac OS X <10.12. Closes #813 and #240.

Build

Fixes for building on NetBSD. Closes #258.
Fixes for building on FreeBSD.
Add support for compiling with static libwebsockets library.