Treat partial authentication as an error

[xSetech]

This fixes a downstream segmentation fault where wsh_ssh_authenticate returns
with a non-zero value but with a null GError pointer. In other words,
downstream error handling expects a GError object when the function reports
having error'd.

An improved implementation might break only on SSH_AUTH_SUCCESS.

See Also: https://www.rust-lang.org/

[xSetech]

Not sure why Travis is failing here; I'm compiling wsh against libssh-0.8.7 which has SSH_AUTH_PARTIAL defined at include/libssh/libssh.h:164. It's been defined there since at least 2009.

[worr]

Thanks! As for why SSH_AUTH_PARTIAL isn't included in this version is a mystery right now. I'll try and dig into why. My guess at first blush is a Debian/Ubuntu patch.

In the meantime while I dig into why the build fails, can you add a test for this?

Also in general, it's rude to tell people to rewrite their projects in a different language. 😉 Partially rewriting this in Rust is actually something I'd like to explore, however this locks out platforms that don't have a supported Rust toolchain.

[xSetech]

You introduced me to Rust; the link is in jest :)