A trip to Bristol was well worth the plane ride across the pond. Banksy, the still-mysterious Bristolian street artist, must be pushing 40, yet the defining tone of his latest show is one of gleeful, establishment-blaming, adolescent despair.It is excellent and I loved it. So many contemporary art exhibitions seem glib in their politics, unimpassioned in their stance, but here Banksy has harnessed his most potent image-making skills to convey a deadly serious message. This pl