offset with queue streams

The offset returned for queue streams is different between offset with
get_stream_info/3 and at/2:

[eclipse 3]: open(queue("abc"), write, a).

yes.
[eclipse 4]: at(a, X), get_stream_info(a, offset, Y).

X = 3
Y = 0
yes.

Also, with this stream, which is in `write' mode, the writes are to the end
of the queue, rather than the start:

[eclipse 5]: write(a, f), get_stream_info(a, name, C).

C = "abcf"
yes.
(should be "fbc" if written to start of queue)