various problems with ssh remotes

[driusan]

There is now preliminary support for ssh remotes (currently only in ls-remote) but it has the following problems:

1. It does not validate host keys to ensure they haven't changed
2. It can only get keys from factotum, not $HOME/.ssh/ (Add basic support for ssh on non-Plan9 platforms #153)
3. It doesn't support password authentication
4. There isn't very good documentation anywhere
5. There is no easy way to get your public key from factotum into your github account

[driusan]

Point 2 is addressed by #153