• Update OpenTTD to the latest stable version 1.9.0
• Collapse per-mirror MASTER_SITES into single CDN entry point: old mirrors do not carry 1.9.0 distfile and I could not find current mirror list, should be OK as new entry point works with "fetch -A": it either does not redirect at all, or sends 301 (permanent), not 302 (temporary) redirect response
• Allow to build with Fluidsynth music driver (off by default)
• Install more complete set of documentation and game files
• Move docfiles installation under `post-install-DOCS-on'
• Add `sdl' to USES list and make pkg-plist file better sorted

PR: 237094 (patchless update request)