git.go
func (r *Repo) checkoutCommit(commitHash string) error {
	var err error
	params := []string{"checkout", commitHash}
	if err = r.gitCmd(params, r.Path); err == nil {
		Logger().Printf("Commit %v checkout done.\n", commitHash)
	}
	return err
}
func (r *Repo) checkoutCommit(commitHash string) error {
	var err error
	params := []string{"checkout", commitHash}
	if err = r.gitCmd(params, r.Path); err == nil {
		Logger().Printf("Commit %v checkout done.\n", commitHash)
	}
	return err
}
// checkoutCommit checks out the specified commitHash.