 u3: refactors cell reallocation, stack struct in u3a_take()
 u3: refactors cell reallocation, stack struct in u3a_take()

ngzax/urbit,urbit/urbit,urbit/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,ngzax/urbit