bricks: Add local_override, a 'dynamic scope' RAII helper.

        finally( const finally & ) = delete;

        finally( const finally & ) = delete;

    };

    };

    template< typename val_t >

    struct local_override

    {

        val_t &value;

        val_t backup;

        local_override( val_t &v, val_t local )

            : value( v ), backup( v )

        {

            value = local;

        }

        ~local_override()

        {

            value = backup;

        }

        local_override( const local_override & ) = delete;

    };

    struct terminate_guard

    struct terminate_guard

    {

    {

        int exit_code;

        int exit_code;