Don't quote absolute path helper commands

Quoting treats the full command as the path to binary, which prevents
arguments from being provided.

According to the [Git documentation][git-docs] arguments
should be accepted. This also [matches the behaviour][git-source] of git
itself.

[git-docs]: https://git-scm.com/docs/api-credentials#_credential_helpers
[git-source]: https://github.com/git/git/blob/ca1b4116483b397e78483376296bcd23916ab553/credential.c#L258-L261

Author: hmarr

src/cred.rs

@@ -257,7 +257,7 @@ impl CredentialHelper {
             self.commands.push(cmd[1..].to_string());
         } else if cmd.starts_with('/') || cmd.starts_with('\\') ||
                   cmd[1..].starts_with(":\\") {
-            self.commands.push(format!("\"{}\"", cmd));
+            self.commands.push(cmd.to_string());
         } else {
             self.commands.push(format!("git credential-{}", cmd));
         }
@@ -522,6 +522,26 @@ echo username=c
                 .execute().is_none());
     }
 
+    #[test]
+    fn credential_helper7() {
+        let td = TempDir::new("git2-rs").unwrap();
+        let path = td.path().join("script");
+        File::create(&path).unwrap().write(br"\
+#!/bin/sh
+echo username=$1
+echo password=$2
+").unwrap();
+        chmod(&path);
+        let cfg = test_cfg! {
+            "credential.helper" => &format!("{} a b", path.display())
+        };
+        let (u, p) = CredentialHelper::new("https://example.com/foo/bar")
+                                      .config(&cfg)
+                                      .execute().unwrap();
+        assert_eq!(u, "a");
+        assert_eq!(p, "b");
+    }
+
     #[test]
     fn ssh_key_from_memory() {
         let cred = Cred::ssh_key_from_memory(