Fix some more spaces-in-paths issues. When using the tags cache directory, the project root is passed to ctags. Escaping this path didn't work correctly when it has spaces: - We remove the quotes around it on *nix because `job_start()` doesn't like those, but then we need to escape the spaces with backslashes otherwise the script doesn't understand those parameters. - Once the escaping is gone in the script, we need to quote them but it looks like sh doesn't like double quotes in the middle of an env var or something, so we need to put the project root in a separate env var.