hgweb: teach WSGI parser about query strings Currently, req.form uses cgi.parse() to populate form data. Depending on the request, form data can come from POST multipart/form-data, application/x-www-form-urlencoded, or the URL query string. Putting all these things into one data structure makes it difficult to reason about how exactly parameters got to the request. It can lead to wonkiness such as pulling parameters from both the URL and POST data. This commit teaches our WSGI request parser about argument data in query strings. We populate fields containing the query string data and only the query string data so it can't be confused with POST data. Differential Revision: https://phab.mercurial-scm.org/D2737