Base64 decoder (see :func:`binascii.a2b_base64`, :func:`base64.b64decode`, etc) no
longer ignores excess data after the first padded quad in non-strict
(default) mode.  Instead, in conformance with :rfc:`4648`, section 3.3, it now ignores
the pad character, "=", if it is present before the end of the encoded data.
