Fix breakage of bitmap scan plan creation for special index operators such

Fix breakage of bitmap scan plan creation for special index operators such
as LIKE.  I oversimplified this code when removing support for plan-time
determination of index operator lossiness back in April --- I had thought
create_bitmap_subplan could stop returning two separate lists of qual
conditions, but it still must so that we can treat special operators
correctly in create_bitmap_scan_plan.  Per report from Rushabh Lathia.