argparse doesn't allow optionals within positionals

[hpaulj]

Python issue http://bugs.python.org/issue14191

Some unix coders are used to freely intermixing optionals and positionals. optparse, which argparse is supposed to replace, parses all of the optionals, and puts everything else in an extras array. This is like parseKnownArgs but with freer intermixing.

A proposed solution is to write a parser.parseIntermixedArgs that does a 2 step parse, first parse the input with only the conditionals arguments, and then parse the extras with the positionals.

[rlidwka]

parse_intermixed_args is ported from python as part of argparse.js 2.0