writing iptc field raises exception oldValues has no len() and/or newValues not iterable

steps to reproduce:

>>> import pyexiv2
>>> import datetime
>>> image = pyexiv2.Image('sample.jpg')
>>> image.readMetadata()
>>> d = datetime.date(2009, 03, 16)
>>> image['Iptc.Application2.DateCreated'] = d
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.5/site-packages/pyexiv2.py", line 648, in __setitem__
    for i in xrange(max(len(oldValues), len(newValues))):
TypeError: object of type 'datetime.date' has no len()
>>>
>>> # deleting the field first, is a possible workaround
... # but triggers another bug
... del(image['Iptc.Application2.DateCreated'])
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
  File "/usr/lib/python2.5/site-packages/pyexiv2.py", line 690, in __delitem__
    for i in xrange(len(oldValues)):
TypeError: object of type 'datetime.date' has no len()
>>> image['Iptc.Application2.DateCreated'] = d
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.5/site-packages/pyexiv2.py", line 659, in __setitem__
    self.__iptcTagsDict[key] = tuple([ConvertToPythonType(tagFamily, typeName, str(v)) for v in newValues])
TypeError: 'datetime.date' object is not iterable

Patch against 0.1.2 attached.
Feel free to modify it, it's rather crude.