There's been a strange turn of developments in that poposal for First Energy Corporation to acquire Allegheny Energy Corporation.     The federal court, in Pittsburgh, is being asked, by the Louisiana Municipal Police Employees Retirement System, to stop the plan for one Western Pennsylvania local area electric utility to puchase the other.     The Louisiana retirement system owns an unspecified amount of Allegheny Energy stock which it asserts would be undervalued in the proposed sale.     The legal action seeks to stop the deal until Allegheny Energy gets more value for its shareholders, possibly by selling Allegheny Energy through a competitive bidding process.     First Energy operates the Pennelec power system locally.