def _checkpoint_out_filenames(self):
        """
        RAxML generates a crapload of checkpoint files so need to
        walk directory to collect names of all of them.
        """
        out_filenames = []
        if self.Parameters['-n'].isOn():
            out_name = str(self.Parameters['-n'].Value)
            walk_root = self.WorkingDir
            if self.Parameters['-w'].isOn():
                walk_root = str(self.Parameters['-w'].Value)
            for tup in walk(walk_root):
                dpath, dnames, dfiles = tup
                if dpath == walk_root:
                    for gen_file in dfiles:
                        if out_name in gen_file and "checkpoint" in gen_file:
                            out_filenames.append(walk_root + gen_file)
                    break

        else:
            raise ValueError, "No output file specified."
        return out_filenames
RAxML generates a crapload of checkpoint files so need to
        walk directory to collect names of all of them.