v5.4.0
Windows: Fix mythread_once() macro with Vista threads.
Bump version to 5.4.0 and soname to 5.4.0.
Build: Prepare to support Automake's subdir-objects.
xzdiff: Add support for .lz files.
xz: Rename --experimental-arm64 to --arm64.
Build: Add support for translated man pages using po4a.