clarified run_sftp: avoid platform_path via careful use of tmp_dir, to support both Windows and Cygwin ssh; discontinued run_scp: use run_sftp instead;

more robust, notably for macOS (see also ff92d6edff2c);

back to plain /tmp (despite 1df53737c59b): relevant for ssh on macOS, to avoid error "unix_listener: path too long for Unix domain socket";

tuned names;

proper order of platforms, to make it work uniformly on all plaform families;

more portable;