[pycrypto] documentation for PKCS1_PSS.py is incorrect, plus minor issue w/ _slowmath.py

[Legrandin]

Mind that the commit makes now the example line be:

>>> signature = signer.sign(key)

Whereas it should really be:

>>>> signature = signer.sign(h)

Because we sign the hash (not the key :-)).

>> https://github.com/dlitz/pycrypto/blob/master/lib/Crypto/Signature/PKCS1_PSS.py
>>
>> In the file on lines 41 & 42 it has:
>>>>>
>>>>> signer = PKCS1_PSS.new(key)
>>>>> signature = PKCS1_PSS.sign(key)
>>
>>
>> The second line is incorrect.  It should be:
>>>>>
>>>>> signature = signer.sign(h)
>
>
> I've committed a fix.  Thanks!