Function _vortex_age

crawl-ref/source/spl-vortex.cc:218–224

}

static int _vortex_age(const actor *caster)
{
    const string name = POLAR_VORTEX_KEY;
    if (caster->props.exists(name.c_str()))
        return you.elapsed_time - caster->props[name.c_str()].get_int();
    return 100; // for permanent vortices
}

// time needed to reach the given radius
static int _age_needed(int r)