In test_argparse.py TestPositionalsActionAppend
with 2 positional args, one that takes 1, the other 2,
parseArgs with 'a b c' produces spam: ['a','b','c'], but python expects
spam: ['a', ['b','c']].
This is because append.js uses 'concat', while python uses 'append'.

Correction: change action/append.js set() to use push()
Merge pull request #37 from hpaulj/positionalAppend

action/append should `push` new values, not `concat`