Auto merge of #2909 - jonathandturner:debug_release_at_bottom, r=alexcrichton

Auto merge of #2909 - jonathandturner:debug_release_at_bottom, r=alexcrichton

Switch to output release/debug after compile

This is similar to https://github.com/rust-lang/cargo/pull/2896 but instead of inline, it puts an indicator at the bottom showing if it was a release or debug build.

```
jturner-23759:cargo jturner$ ./target/release/cargo build
Finished debug (unoptimized + debuginfo) build.
jturner-23759:cargo jturner$ ./target/release/cargo build --release
Finished release (optimized) build.
```