Boris Smolensky's budget repertory production of "Murder at Priorswell Manor" is looking decidedly shaky. The cast are more interested in their egos than the play and life imitates art when Boris's wife, Renee, is murdered on stage. Simon Brett's hilarious text, a worthy companion to his Charles Paris theatrical thriller novels, ruthlessly satirizes the politics of the inept company and the numerous red herrings keep the audience guessing until the final moments of the play.5 women, 3 men