DefaultVariableArity implementation

The following parameter is supposed to get many parameters to pass to an
external software.

	// JS Parameters
	@Parameter(names = "-J", description = "Parameters to be passed
to Google Closure Compiler", variableArity = true)
	public List<String> closureOpts = new ArrayList<String>();

So my app will be called like this

	foo -J --compilation_level WHITESPACE_ONLY
--language_in=ECMASCRIPT5 -bar baz -faz -J --more-options

Judging by the documentation:

> You can specify that a parameter can receive an indefinite number of
> parameters, up to the next option. For example:

I was expecting to get

	{ "--compilation_level", "WHITESPACE_ONLY",
"--language_in=ECMASCRIPT5", "--more-options" }

Instead I've received

ParameterException for "Unknown options".

If I set AcceptUnknownOptions to true, it still does not work as I've
expected and the list is not populated at all.

I believe correct behaviour should be to interpret all of the parameters
after a VariableArity parameter until next VALID parameter as raw values
and add them to the list.

This patch does that and gives the result I expected.

The expected result could also be achived by deriving our  MyOptions
class from IVariableArity (see JCommander.java:824) but I believe our
options class is not the appropriate place to change this behaviour.