Fix the external special remotes git-annex-remote-ipfs,
git-annex-remote-torrent and the example.sh template to correctly support
filenames with spaces.
This commit was sponsored by John Peloquin on Patreon.
Useful for things like ipfs that don't use regular urls.
An external special remote can add a regular url to a key, and then
git-annex get will download it from the web. But for ipfs, we want to
instead tell git-annex that the uri uses OtherDownloader. Before this
change, the external special remote protocol lacked a way to do that.