ECB mode accepts IV

[Legrandin]

The following code works fine:

    from Crypto.Cipher import AES
    ecb_cipher = AES.new(b"\x00" * 16, AES.MODE_ECB, b"\x00" * 16)

That is quite bad: a user might have wanted to actually set up the CBC mode (given the presence of the IV).
However, PyCrypto does not complain and creates the ECB cipher by ignoring the IV.

Instead, presence of the IV should lead to an exception when the mode is ECB.

[Darsey Litzenberger (dlitz)]

Fixed: https://github.com/dlitz/pycrypto/commit/8dbe0dc3eea5c689d4f76b37b93fe216cf1f00d4