Don't respect [source] .cargo/config configuration

That just messes with us actually updating sources. Instead we want to go
straight to crates.io all the time to vendor new crates.

Closes #23

Cargo.toml

@@ -12,6 +12,6 @@ filesystem.
 """
 
 [dependencies]
-cargo = "0.18"
+cargo = { git = 'https://github.com/rust-lang/cargo' }
 rustc-serialize = "0.3"
 env_logger = "0.4"

src/main.rs

@@ -32,7 +32,20 @@ struct Options {
 
 fn main() {
     env_logger::init().unwrap();
-    let config = Config::default().unwrap();
+
+    // We're doing the vendoring operation outselves, so we don't actually want
+    // to respect any of the `source` configuration in Cargo itself. That's
+    // intended for other consumers of Cargo, but we want to go straight to the
+    // source, e.g. crates.io, to fetch crates.
+    let config = {
+        let config_orig = Config::default().unwrap();
+        let mut values = config_orig.values().unwrap().clone();
+        values.remove("source");
+        let config = Config::default().unwrap();
+        config.set_values(values).unwrap();
+        config
+    };
+
     let args = env::args().collect::<Vec<_>>();
     let result = cargo::call_main_without_stdin(real_main, &config, r#"
 Vendor all dependencies for a project locally

tests/vendor.rs

@@ -206,3 +206,35 @@ fn two_lockfiles() {
     run(Command::new("cargo").arg("build").current_dir(&dir.join("foo")));
     run(Command::new("cargo").arg("build").current_dir(&dir.join("bar")));
 }
+
+#[test]
+fn revendor_with_config() {
+    let dir = dir();
+
+    file(&dir, "Cargo.toml", r#"
+        [package]
+        name = "foo"
+        version = "0.1.0"
+
+        [dependencies]
+        bitflags = "=0.7.0"
+    "#);
+    file(&dir, "src/lib.rs", "");
+
+    run(&mut vendor(&dir));
+    let lock = read(&dir.join("vendor/bitflags/Cargo.toml"));
+    assert!(lock.contains("version = \"0.7.0\""));
+
+    add_vendor_config(&dir);
+    file(&dir, "Cargo.toml", r#"
+        [package]
+        name = "foo"
+        version = "0.1.0"
+
+        [dependencies]
+        bitflags = "=0.8.0"
+    "#);
+    run(&mut vendor(&dir));
+    let lock = read(&dir.join("vendor/bitflags/Cargo.toml"));
+    assert!(lock.contains("version = \"0.8.0\""));
+}