Calls to tkinter.filedialog.askdirectory() throw a KeyError if any of 
the options (title, text, bitmap, default, strings) are not provided.

Previously saying "askdirectory()" with no arguments would open a file 
browser window. Since all other functions in filedialog still function 
with no arguments this seems like an error. (Actually askopenfiles() 
seems to be broken too, saying "IOError: [Errno 2] No such file or 
directory: '{'")