In stage 2, don't touch the .viminfo file and don't create swap files.

I've seen the tags update clobbering my `~/.viminfo` history, especially because stage 2 doesn't run with my `.vimrc` settings and therefore with default sizes for the retained history.
Also, turn off swap files; though stage 2 doesn't `:edit` any files, don't run the risk of accidentally littering the file system with swap files.