No error for bare asterisk after *args

[JukkaL]

The following code is accepted by the parser, even though Python gives a syntax error:

def f(*x, *, y = 1): pass

The code should generate a parse error.

[doboy]

I'll take this

[JukkaL]

This is still up for grabs.

[etrepum]

This is an interesting one because there are cases that Python accepts that mypy doesn't as well, such as this:

def f(*x, y): pass

Also, notably, mypy's stub for print uses a syntax that is invalid in Python!

>>> def print_(*values, *, sep=u' ', end=u'\n', file=None): pass
  File "<stdin>", line 1
    def print_(*values, *, sep=u' ', end=u'\n', file=None): pass
                        ^
SyntaxError: invalid syntax

I'm looking into it. I'm mostly done with a patch, but want to figure out what else mypy gets wrong here :)