The "pushres" and "pusherr" response types currently call
proto.restore() in the HTTP protocol. This completes the pairing
with proto.redirect() that occurs in the @wireprotocommand
functions. (But since the SSH protocol has a no-op redirect(),
it doesn't bother calling restore() because it would also be
a no-op.)
Having the disconnect between these paired calls is very confusing.
Knowing that you must use proto.redirect() if returning a "pushres"
or a "pusherr" is even wonkier.
We replace this confusing code with our new context manager for
[maybe] capturing output.
The "pushres" and "pusherr" types have gained an "output" argument
to their constructor and an attribute to hold captured data. The
HTTP protocol now retrieves output from these objects.
.. api::
``wireproto.pushres`` and ``wireproto.pusherr`` now explicitly track stdio output.