url: Remove the proxy env variables only when needed (issue2451) This is an attempt to fix issue 2451 and its duplicates (2599 and 2949, AFAIK). Its main idea is that it is only necessary to clean the proxy environment variables *when* http_proxy is set in the config file (since it takes precedence over the environment variables). Otherwise, hg shouldn't bother with them, since they will most likely be used to reach the server.