how to handle crates that require extra dependencies (specifically shared libraries)

[codyps]

https://github.com/jmesmon/rust-systemd/issues/13 has some details.

Essentially: rust-systemd depends on libsystemd.so, which it currently can build for travis-ci via a shell script run prior to cargo build invocation. Due to this being a shared library, building with build.rs isn't really correct as the library search path doesn't include OUT_DIR.

We'd like a way to be compatible with clippy-service, and it seems likely we'll need changes to clippy-service (or perhaps cargo) to get there. This issue above has some options. I'd appreciate your input on what the right course of action here is with respect to clippy-service (or maybe there's a good way to do this already that I've overlooked!).

[codyps]

Might be a dup of #23