This is mainly a compatibility release.
In 0.42, some languages or databases weren't detected properly on some platforms or needed tweaks to build against. This release should resolve most or all of those issues.
It's also now possible to build rudiments, the client library and command line apps under mingw32 and run them on Windows without Cygwin.
You can also now set the character set in the sqlrelay.conf file for all databases that support it.