hgweb: port archive command to modern response API Well, I tried to go with PEP 3333's recommendations and only allow our WSGI application to emit data via a response generator. Unfortunately, the "archive" command calls into the zipfile and tarfile modules and these operator on file objects and must send their data to an object with write(). There's no easy way turn these write() calls into a generator. So, we teach our response type how to expose a file object like object that can be used to write() output. We try to keep the API consistent with how things work currently: callers must call a setbody*(), then sendresponse() to trigger sending of headers, and only then can they get a handle on the object to perform writing. This required overloading the return value of @webcommand functions even more. Fortunately, we're almost completely ported off the legacy API. So we should be able to simplify matters in the near future. A test relying on this functionality has also been updated to use the new API. Differential Revision: https://phab.mercurial-scm.org/D2792