If you haven’t been following the step-by-step progress of the ongoing Pershing Park case (that’s the 2002 mass arrests of some 400 protesters by D.C. police, still playing out in endless legal wrangling), you might have missed the big development that surfaced Wednesday. City Paper’s Jason Cherkis has been all over this story for … forever, and yesterday he reported that a new affidavit from veteran D.C. Police Det. Paul Hustler points the finger…