add options to Git.ListRefs

this is a breaking change, but this was only recently added so I'm not
too worried.  This also seems the best way to handle sub-namespaces on
this method.

github/git_refs.go

@@ -62,17 +62,28 @@ func (s *GitService) GetRef(owner string, repo string, ref string) (*Reference,
 	return r, resp, err
 }
 
+// ReferenceListOptions specifies optional parameters to the
+// GitService.ListRefs method.
+type ReferenceListOptions struct {
+	Type string `url:"-"`
+}
+
 // ListRefs lists all refs in a repository.
 //
 // GitHub API docs: http://developer.github.com/v3/git/refs/#get-all-references
-func (s *GitService) ListRefs(owner string, repo string) ([]*Reference, *Response, error) {
-	u := fmt.Sprintf("repos/%v/%v/git/refs", owner, repo)
+func (s *GitService) ListRefs(owner, repo string, opt *ReferenceListOptions) ([]Reference, *Response, error) {
+	var u string
+	if opt != nil && opt.Type != "" {
+		u = fmt.Sprintf("repos/%v/%v/git/refs/%v", owner, repo, opt.Type)
+	} else {
+		u = fmt.Sprintf("repos/%v/%v/git/refs", owner, repo)
+	}
 	req, err := s.client.NewRequest("GET", u, nil)
 	if err != nil {
 		return nil, nil, err
 	}
 
-	var rs []*Reference
+	var rs []Reference
 	resp, err := s.client.Do(req, &rs)
 	if err != nil {
 		return nil, resp, err

github/git_refs_test.go

@@ -62,29 +62,29 @@ func TestGitService_ListRefs(t *testing.T) {
 		      "ref": "refs/heads/branchA",
 		      "url": "https://api.github.com/repos/o/r/git/refs/heads/branchA",
 		      "object": {
-		        "type": "commit",
-		        "sha": "aa218f56b14c9653891f9e74264a383fa43fefbd",
-		        "url": "https://api.github.com/repos/o/r/git/commits/aa218f56b14c9653891f9e74264a383fa43fefbd"
+			"type": "commit",
+			"sha": "aa218f56b14c9653891f9e74264a383fa43fefbd",
+			"url": "https://api.github.com/repos/o/r/git/commits/aa218f56b14c9653891f9e74264a383fa43fefbd"
 		      }
 		    },
 		    {
 		      "ref": "refs/heads/branchB",
 		      "url": "https://api.github.com/repos/o/r/git/refs/heads/branchB",
 		      "object": {
-		        "type": "commit",
-		        "sha": "aa218f56b14c9653891f9e74264a383fa43fefbd",
-		        "url": "https://api.github.com/repos/o/r/git/commits/aa218f56b14c9653891f9e74264a383fa43fefbd"
+			"type": "commit",
+			"sha": "aa218f56b14c9653891f9e74264a383fa43fefbd",
+			"url": "https://api.github.com/repos/o/r/git/commits/aa218f56b14c9653891f9e74264a383fa43fefbd"
 		      }
 		    }
 		  ]`)
 	})
 
-	refs, _, err := client.Git.ListRefs("o", "r")
+	refs, _, err := client.Git.ListRefs("o", "r", nil)
 	if err != nil {
 		t.Errorf("Git.ListRefs returned error: %v", err)
 	}
 
-	want := []*Reference{
+	want := []Reference{
 		{
 			Ref: String("refs/heads/branchA"),
 			URL: String("https://api.github.com/repos/o/r/git/refs/heads/branchA"),
@@ -109,6 +109,27 @@ func TestGitService_ListRefs(t *testing.T) {
 	}
 }
 
+func TestGitService_ListRefs_options(t *testing.T) {
+	setup()
+	defer teardown()
+
+	mux.HandleFunc("/repos/o/r/git/refs/t", func(w http.ResponseWriter, r *http.Request) {
+		testMethod(t, r, "GET")
+		fmt.Fprint(w, `[{"ref": "r"}]`)
+	})
+
+	opt := &ReferenceListOptions{Type: "t"}
+	refs, _, err := client.Git.ListRefs("o", "r", opt)
+	if err != nil {
+		t.Errorf("Git.ListRefs returned error: %v", err)
+	}
+
+	want := []Reference{{Ref: String("r")}}
+	if !reflect.DeepEqual(refs, want) {
+		t.Errorf("Git.ListRefs returned %+v, want %+v", refs, want)
+	}
+}
+
 func TestGitService_CreateRef(t *testing.T) {
 	setup()
 	defer teardown()