Add new fake instr to hold intperpreter state.  This instr is destined to only be instr 0 of the linearized instr list used only by the interpreter.  It removes all remaining IRScope state knowledge from interpreter (not currently hooked up).
Boo. nested closures need unmolested parent scopes based on passes which may replace parent variables with temp vars.  We cannot use this simpler approach and will end up going the original full-clone route.  Commented out cloning in prepareInstructions