Gas prices keep going nowhere but down.  The Triple-A stations survey shows the national average price for regular is down to four dollars and seven cents a gallon, a penny lower than yesterday.  Twenty-nine states have statewide averages below for dollars a gallon, including Minnesota at about $3.90 a gallon. Missouri is still the leader, falling another penny to three-63 a gallon.  California’s the most expensive at five-71 a gallon but that’s two cents lower than yesterday.