The attached patch resolves test failues in test_asynchat and
test_asyncore.

The asynchat failure was due to interpolating a byte string into a
unicode string using %s.  This resulted in a b'' byte representation
in the final string.  The fix is to use string constants instead of
byte constants.  The result is encoded to bytes later on.

The asyncore failure was due to an explicit isinstance(data, bytes)
check on the result of recv.  The actual type in this case was buffer.
I've removed the check since the next line calls

data.replace(b'\n', b'')

This all should fail for anything thats not a buffer or bytes.