[Python-3000] Four new failing tests

["Martin v. Löwis"]

> ======================================================================
> ERROR: test_char_write (__main__.TestArrayWrites)
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "Lib/test/test_csv.py", line 648, in test_char_write
>     a = array.array('u', string.letters)
> ValueError: string length not a multiple of item size

I think some decision should be made wrt. string.letters.

Clearly, string.letters cannot reasonably contain *all* letters
(i.e. all characters of categories Ll, Lu, Lt, Lo). Or can it?

Traditionally, string.letters contained everything that is a letter
in the current locale. Still, computing this string might be expensive
assuming you have to go through all Unicode code points and determine
whether they are letters in the current locale.

So I see the following options:
1. remove it entirely. Keep string.ascii_letters instead
2. remove string.ascii_letters, and make string.letters to be
   ASCII only.
3. Make string.letters contain all letters in the current locale.
4. Make string.letters truly contain everything that is classified
   as a letter in the Unicode database.

Which one should happen?

Regards,
Martin