url: add HTTP handler that uses a proxied socket Now that we have a socket proxy that can log I/O, we need to teach mechanisms that open URLs how to use it. We invent a custom HTTP handler class that knows how to proxy sockets as soon as they are opened. We teach the high-level opener() to accept logging arguments so a logging HTTP handler can be constructed. We don't yet support intercepting HTTPS sockets because I don't want to go down that rabbit hole. For the record, the urllib API is crazy and it took way too long to figure out at what levels I needed to plug in to modify the socket. # no-check-commit because we must name http_open that way Differential Revision: https://phab.mercurial-scm.org/D2722