DES MOINES — As certain as opening day promises of bipartisanship and adjournment day boasts of accomplishments, Iowa legislative sessions are marked by attempts to change the four-decade-old law that requires nickel deposits on pop and beer cans.At least nine measures have been introduced this year proposing changes in the “bottle bill” law that was enacted in the late 1970s to reduce roadside littering.Legislators and lobbyists involved in the discussion cautiously suggest there’s been progress this time.“I think there are good prospects of getting this out of the Senate this year,” said Sen.