Problem: proto::message is checked into the repo

However, it is generated during build-time and therefor is
unnecessary to be kept around in the repository.

There are two potential solutions for this problem:

1. Don't generate it build-time and use a checked-in version
2. Don't check it in.

Solution: don't check it in

The reason why I picked this solution is because it is, generally
speaking, less error-prone as it prevents "I forgot to regenerate
files" type of situations.

.gitignore

@@ -0,0 +1 @@
+src/proto/message.rs

build.rs

@@ -1,6 +1,7 @@
 extern crate protoc_rust;
 
 fn main() {
+    println!("cargo:rerun-if-changed=proto/message.proto");
     protoc_rust::run(protoc_rust::Args {
         out_dir: "src/proto",
         input: &["proto/message.proto"],