Add cargo-0.60.0 as a new benchmark.

I obtained the code with:
```
target/release/collector download -c primary crate cargo 0.60.0
```

`cargo-0.60.0/perf-config.json` and `cargo-0.60.0/0-println.patch` are
based on the corresponding files in `cargo/`.

`cargo-0.60.0` is quite a bit slower to compile than `cargo`. Times for
`full` builds of the final crate on my machine:
```
		cargo   cargo-0.60.0
cargo check 	4.26    6.92
cargo debug 	10.13   19.72
cargo opt 	17.59   35.67
```
And to run the entire benchmark (including compiling all crates):
```
cargo:        Check  real 18.46 user  84.04 sys 18.01
cargo-0.60.0: Check  real 18.16 user 100.21 sys 13.45
cargo:        Debug  real 25.98 user 163.99 sys 21.99
cargo-0.60.0: Debug  real 32.92 user 205.82 sys 18.37
cargo:        Opt    real 38.28 user 450.19 sys 20.37
cargo-0.60.0: Opt    real 55.54 user 585.34 sys 19.06
```

`cargo` will be removed soon.

Author: nnethercote

collector/benchmarks/README.md

@@ -16,6 +16,8 @@ They mostly consist of real-world crates.
 
 - **cargo**: The Rust package manager. An important program in the Rust
   ecosystem.
+- **cargo-0.60.0**: The Rust package manager. A large program, and an important
+  one in the Rust ecosystem.
 - **clap-rs**: A command line argument parser. A crate used by many Rust
   programs.
 - **cranelift-codegen**: The largest crate from a code generator. Used by

collector/benchmarks/cargo-0.60.0/0-println.patch

@@ -0,0 +1,12 @@
+diff --git a/src/cargo/sources/path.rs b/src/cargo/sources/path.rs
+index cc1c9874..4abbd75e 100644
+--- a/src/cargo/sources/path.rs
++++ b/src/cargo/sources/path.rs
+@@ -54,6 +54,7 @@ impl<'cfg> PathSource<'cfg> {
+     }
+ 
+     pub fn preload_with(&mut self, pkg: Package) {
++        println!("testing");
+         assert!(!self.updated);
+         assert!(!self.recursive);
+         assert!(self.packages.is_empty());

collector/benchmarks/cargo-0.60.0/CHANGELOG.md

@@ -0,0 +1,5 @@
+# Contributing to Cargo
+
+Contributing documentation has moved to the **[Cargo Contributor Guide]**.
+
+[Cargo Contributor Guide]: https://rust-lang.github.io/cargo/contrib/