Combine package specifications' limitations.

        Args:
            specs (list of PackageSpec): the package specifications.

        Returns:
            list of PackageSpec: the new, merged list of PackageSpec.

def combine(specs):
        """
        Combine package specifications' limitations.

        Args:
            specs (list of PackageSpec): the package specifications.

        Returns:
            list of PackageSpec: the new, merged list of PackageSpec.
        """
        new_specs = {}
        for spec in specs:
            if new_specs.get(spec, None) is None:
                new_specs[spec] = spec
            else:
                new_specs[spec].add(spec)
        return list(new_specs.values())