Improve obscure error message

[005]

i just got an error
RuntimeError: unexpected attribute data type: 23, expected 26
@ File "asyncpg/protocol/codecs/base.pyx", line 155,

which confused me. actually it happens when i try to select whole record.

create table mytab (a int);
insert into mytab values (1);
select mytab from mytab;

it can't decode "record" and fails with "unexpected attribute data type: 23, expected 26"

[elprans]

That's an actual bug. I just pushed a fix. The error message should be better now too. Thanks for the report!