httppeer: add support for httppostargs when we're sending a file This is probably only used in the 'unbundle' command, but the code ended up being cleaner to make it generic and treat *all* httppostargs with a non-args request body as though they were file-like in nature. It also means we get test coverage more or less for free. A previous version of this change didn't use io.BytesIO, and it was a lot more complicated. This also fixes a server-side bug, so anyone using httppostargs should update all of their servers to this revision or later *before* this gets to their clients, otherwise servers will hang trying to over-read the POST body. Differential Revision: https://phab.mercurial-scm.org/D231