Spirit Airlines is on shaky footing after JetBlue Airways' proposed 3.8billiontakeoverofthebudgetcarrierwasblockedbyafederaljudgethisweek.Industry−watcherssaythecarriercouldbeforcedtocutitsalreadylowfaresevenmore.SomeWallStreetanalystsarguethediscountcarriercouldhavetorestructure,ifnotliquidate.Spirit′ssharesfell475.74 a share. Spirit, whose last pr ...