prepare_vimvar(int idx, typval_T *save_tv)
{
    *save_tv = vimvars[idx].vv_tv;
    vimvars[idx].vv_str = NULL;  // don't free it now
    if (vimvars[idx].vv_tv_type == VAR_UNKNOWN)
	hash_add(&vimvarht, vimvars[idx].vv_di.di_key);
}
prepare_vimvar(int idx, typval_T *save_tv)
{
    *save_tv = vimvars[idx].vv_tv;
    vimvars[idx].vv_str = NULL;   
    if (vimvars[idx].vv_tv_type == VAR_UNKNOWN)
	hash_add(&vimvarht, vimvars[idx].vv_di.di_key);
}