Type checker rejects call with both *args and a keyword arg

[JukkaL]

The following code is not accepted by the type checker, even though it's arguably valid:

def f(a, x=1): pass
f(*[1], x=2)   # Error: multiple values for keyword argument "x"

The type checker should probably not complain about multiple argument values if one of the values is from a *arg.

The limitation can be worked around by replacing keyword args with dict args (**args).

[JukkaL]

Also, this should work but isn't accepted:

def f(a, x): pass
f(x=2, *[1])   # Error: multiple values for keyword argument "x"

[JukkaL]

Actually, maybe the first example should not be valid, since we can't check that there are no multiple argument values due to not knowing the length of the *args list.

We can revisit this later if it turns out to be problematic.

[JukkaL]

I committed a partial fix now that fixes the parser issue.