allinone - add args_default_to_positional optional arg
python issue9334
allinone
  - implement checking on nargs values during addArgument
  - ArgumentParser._check_args
     call formatter _format_args
        error if nargs is not good string or integer
        tentative error if nargs is negative
        error if nargs does match with array metavar
  - pformat - error like py if format string and args don't match


http://bugs.python.org/issue16970
http://bugs.python.org/issue9849

test_nargsvalues - test these changes