Previous XQuartz releases (up to 2.8.2) were .dmg; v2.8.3 and 2.8.4 have been .pkg, and FlatPkgUnpacker will fail to find the downloaded .pkg when the flat_pkg_path is %pathname%/XQuartz.pkg (since it does not exist; %pathname% itself is /some/path/to/cache/XQuartz-version.pkg).
Previous XQuartz releases (up to 2.8.2) were .dmg; v2.8.3 and 2.8.4 have been .pkg, and FlatPkgUnpacker will fail to find the downloaded .pkg when the flat_pkg_path is %pathname%/XQuartz.pkg (since it does not exist; %pathname% itself is /some/path/to/cache/XQuartz-version.pkg).