Upstream Style.copy constructor regression breaks _Openpyxl2Writer

[neirbowj]

Starting with openpyxl 2.2.0, various tests in pandas.io.tests.test_excel fail with tracebacks similar to this one.

======================================================================
ERROR: test_basics_with_nan (pandas.io.tests.test_excel.Openpyxl2Tests)
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Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/pandas/io/tests/test_excel.py", line 1229, in wrapped
    orig_method(self, *args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pandas/io/tests/test_excel.py", line 641, in test_basics_with_nan
    self.frame.to_excel(path, 'test1')
  File "/usr/local/lib/python2.7/site-packages/pandas/core/frame.py", line 1267, in to_excel
    startrow=startrow, startcol=startcol)
  File "/usr/local/lib/python2.7/site-packages/pandas/io/excel.py", line 778, in write_cells
    xcell.style = xcell.style.copy(**style_kwargs)
  File "/usr/local/lib/python2.7/site-packages/openpyxl/styles/styleable.py", line 107, in style
    protection=self.protection
  File "/usr/local/lib/python2.7/site-packages/openpyxl/styles/__init__.py", line 42, in __init__
    self._font = font
  File "/usr/local/lib/python2.7/site-packages/openpyxl/descriptors/base.py", line 35, in __set__
    raise TypeError('expected ' + str(self.expected_type))
TypeError: expected <class 'openpyxl.styles.fonts.Font'>

pandas.io.excel._Openpyxl2Writer.write_cells uses openpyxl.styles.Style.copy to merge newly specified style data with style data on existing cells. Sadly, the obvious workaround—iterate over the fields of the Style object and use them to build an updated Style object—won't work either without additional coddling, because the fields don't reliably return the native object that the Style constructor demands.

>>> from openpyxl.styles import Style
>>> s0 = Style()
>>> s1 = Style(fill=s0.fill)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/obrienjw/venv/py27-openpyxl220/lib/python2.7/site-packages/openpyxl-2.2.0-py2.7.egg/openpyxl/styles/__init__.py", line 43, in __init__
    self._fill = fill
  File "/Users/obrienjw/venv/py27-openpyxl220/lib/python2.7/site-packages/openpyxl-2.2.0-py2.7.egg/openpyxl/descriptors/base.py", line 35, in __set__
    raise TypeError('expected ' + str(self.expected_type))
TypeError: expected <class 'openpyxl.styles.fills.Fill'>

(See upstream issue: 444 copy() method on Style object raises TypeError)

[jreback]

replaced by #10125