Auto merge of #1267 - aidanhs:aphs-better-error-on-rustup.sh, r=alexcrichton
Auto merge of #1267 - aidanhs:aphs-better-error-on-rustup.sh, r=alexcrichton

Give a hint of what to do if rustup is installed

cc https://github.com/rust-lang-nursery/rustup.rs/issues/618#issuecomment-337018936

nodakai/rustup.rs,rust-lang/rustup,inejge/rustup.rs,rust-lang/rustup,inejge/rustup.rs,nodakai/rustup.rs,inejge/rustup.rs,inejge/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,inejge/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs