Download

A new feature requiring lftp installed. It assembles an lftp mirror
command to download all changes from the FTP server into your current
working tree.

It aborts on untracked files, because the mirror command is deleting files that are not on the server.

I would like to introduce code around the big "pull feature" step by step. This is the first step, a simple download. If you think it's fine, then I would go ahead with the pull action and maybe the bootstrap action. We could have that for version 1.0. The check-for-remote-changes feature is independent code but would complete the workflow (push, oh conflict, pull, push). It requires more coding as discussed in #97.

By the way, picking the necessary code pieces is a good code review and cleanup. I found some little artifacts of my big merge-everything-together. The downside is that all references to the original authors are lost. The original download code comes from @drench.