Correct 'help' when argumentDefault and prefixChars options are used

argparse.js fails 2 help related tests in `test_argparse.py`

`TestParserDefault42` sets a parser `argumentDefault`
The error is that the namespace includes `{help: 42, version: 42}`
Correction: add `defaultValue: $$.SUPPRESS` when defining --help and --version
in ArgumentParser().

`TestOptionalsAlternatePrefixCharsAddedHelp` sets `prefixChars`.
If `prefixChars` does not include '-', setting `['-h','--help']` gives an error.
Correction: set a `defaultPrefix` that is either '-' or the first `prefixChar`,
and use this instead of '-h'