Should not have to specify crates-io registry URL to replace-with

Since cargo knows crates-io's registry URL and, anyway, you're trying to
say that you don't want to use crates-io.

src/cargo/sources/config.rs

@@ -146,6 +146,9 @@ a lock file compatible with `{orig}` cannot be generated in this situation
             path.push(s);
             srcs.push(try!(SourceId::for_directory(&path)));
         }
+        if name == "crates-io" && srcs.is_empty() {
+            srcs.push(try!(SourceId::crates_io(self.config)));
+        }
 
         let mut srcs = srcs.into_iter();
         let src = try!(srcs.next().chain_error(|| {

tests/bad-config.rs

@@ -689,7 +689,6 @@ fn bad_source_config2() {
         .file("src/lib.rs", "")
         .file(".cargo/config", r#"
             [source.crates-io]
-            registry = 'http://example.com'
             replace-with = 'bar'
         "#);
 
@@ -721,7 +720,6 @@ fn bad_source_config3() {
         .file("src/lib.rs", "")
         .file(".cargo/config", r#"
             [source.crates-io]
-            registry = 'http://example.com'
             replace-with = 'crates-io'
         "#);
 
@@ -752,7 +750,6 @@ fn bad_source_config4() {
         .file("src/lib.rs", "")
         .file(".cargo/config", r#"
             [source.crates-io]
-            registry = 'http://example.com'
             replace-with = 'bar'
 
             [source.bar]
@@ -788,7 +785,6 @@ fn bad_source_config5() {
         .file("src/lib.rs", "")
         .file(".cargo/config", r#"
             [source.crates-io]
-            registry = 'http://example.com'
             replace-with = 'bar'
 
             [source.bar]
@@ -842,7 +838,6 @@ fn bad_source_config6() {
         .file("src/lib.rs", "")
         .file(".cargo/config", r#"
             [source.crates-io]
-            registry = 'http://example.com'
             replace-with = ['not', 'a', 'string']
         "#);
 

tests/cargotest/support/registry.rs

@@ -49,7 +49,6 @@ pub fn init() {
             token = "api-token"
 
         [source.crates-io]
-        registry = 'https://wut'
         replace-with = 'dummy-registry'
 
         [source.dummy-registry]

tests/directory.rs

@@ -20,7 +20,6 @@ fn setup() {
     t!(fs::create_dir(&root.join(".cargo")));
     t!(t!(File::create(root.join(".cargo/config"))).write_all(br#"
         [source.crates-io]
-        registry = 'https://wut'
         replace-with = 'my-awesome-local-registry'
 
         [source.my-awesome-local-registry]

tests/local-registry.rs

@@ -15,7 +15,6 @@ fn setup() {
     t!(fs::create_dir(&root.join(".cargo")));
     t!(t!(File::create(root.join(".cargo/config"))).write_all(br#"
         [source.crates-io]
-        registry = 'https://wut'
         replace-with = 'my-awesome-local-registry'
 
         [source.my-awesome-local-registry]
@@ -274,7 +273,6 @@ fn invalid_dir_bad() {
         .file("src/lib.rs", "")
         .file(".cargo/config", r#"
             [source.crates-io]
-            registry = 'https://wut'
             replace-with = 'my-awesome-local-directory'
 
             [source.my-awesome-local-directory]