Swan theatre, Stratford-upon-AvonIsobel McArthur gives a giddy fresh spin to Thomas Heywood's 16th-century romp which sends a Cornish landlady, in her repurposed bar, to sea 'Not everything is good because it's old," sighs the prologue to Isobel McArthur's debut RSC show. Its launchpad is a rousing Elizabethan play by Thomas Heywood, an all-action yarn about a Plymouth barmaid turned pirate captain. The last RSC prod…