Message2455

PyComplex method complex_new was not checking for
keyword arguments making it possible to do:
  complex(imag=3,imag=4) or
  complex(real=5, real=7)

This fix eliminates this by throwing a SyntaxError like
Python.

>>> complex(imag=4,imag=3)
Traceback (innermost last):
  File "<console>", line 1, in ?
  File "None", line None
SyntaxError: duplicate keyword argument.
>>> complex(real=4,real=3)
Traceback (innermost last):
  File "<console>", line 1, in ?
  File "None", line None
SyntaxError: duplicate keyword argument.
>>> complex(imag=4)
4j
>>> complex(real=4)
(4+0j)
>>> complex(real=4,imag=98)
(4+98j)
>>>