This diff fixes running the pakinstaller (the menu for downloading paksets on first launch if none are present) on OpenBSD where I'm developing a port of simutrans. Before this patch, running simutrans without a pre-existing directory
~/simutrans/ would fail on first run (not second because the directory exists then). Also fixes the downloading of other/multiple paksets. An alternative approach would be to include mkdir in dr_chdir, and/or error handling for dr_chdir.
Fixes things on OpenBSD, but the solution should apply to *nix (Linux, other BSDs).
Thank you, included.