
  -spec process_flag(Pid, Flag, Value) -> OldValue
                        when
                            Pid :: pid(),
                            Flag :: save_calls,
                            Value :: non_neg_integer(),
                            OldValue :: non_neg_integer().

  Sets certain flags for the process Pid, in the same manner as 
  process_flag/2. Returns the old value of the flag. The valid
  values for Flag are only a subset of those allowed in 
  process_flag/2, namely save_calls.

  Failure: badarg if Pid is not a local process.
