Disable replace references and grafts while running

The algorithm we use relies on traversing all of history, and in the
correct order. Replace references and grafts screw up that order. So
disable both of them while running.

Author: mhagger

git/git.go

@@ -97,9 +97,21 @@ func NewRepository(path string) (*Repository, error) {
 	return repo, nil
 }
 
-func (repo *Repository) gitCommand(args ...string) *exec.Cmd {
+func (repo *Repository) gitCommand(callerArgs ...string) *exec.Cmd {
+	// Disable replace references when running our commands:
+	args := []string{"--no-replace-objects"}
+
+	args = append(args, callerArgs...)
+
 	cmd := exec.Command("git", args...)
-	cmd.Env = append(os.Environ(), "GIT_DIR="+repo.path)
+
+	cmd.Env = append(
+		os.Environ(),
+		"GIT_DIR="+repo.path,
+		// Disable grafts when running our commands:
+		"GIT_GRAFT_FILE="+os.DevNull,
+	)
+
 	return cmd
 }