bug fix: there is no way to save or load a file that has a python 2 string name

[chfw]

I am not sure the reason why those assertions are there in the first place. Given Python heavily uses duct typing, I would say please do it in C++.

And it prevent you from doing the following basic things using python 2. Yes, it is a bug because odfpy v0.9.6 allows you do the following.

>>> from odf.opendocument import load
>>> load("abc.ods")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "odf/opendocument.py", line 960, in load
    or 'BufferedReader' in repr(odffile)  or 'BytesIO' in repr(odffile))
AssertionError
>>> from odf.opendocument import OpenDocumentSpreadsheet
>>> book=OpenDocumentSpreadsheet()
>>> book.write("abc.ods")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "odf/opendocument.py", line 589, in write
    assert('wb' in repr(outputfp) or 'BufferedWriter' in repr(outputfp)  or 'BytesIO' in repr(outputfp))
AssertionError
>>>