[win32] Deleting directories fails

Test suite fails on windows after patch for supporting symlinks. This will show up when the user tries to delete a page + sub-pages.

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ERROR: Test Dir object
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Traceback (most recent call last):
 File "C:\Documents and Settings\jkarssen\My Documents\download\zim-0.47\tests\
fs.py", line 253, in testDir
   dir.remove_children()
 File "C:\Documents and Settings\jkarssen\My Documents\download\zim-0.47\zim\fs
.py", line 633, in remove_children
   for root, dirs, files in os.walk(self.encodedpath, topdown=False, followlink
s=False):
TypeError: walk() got an unexpected keyword argument 'followlinks'