hgweb: return content iterator instead of using write() callable This is a new version of 4879468fa28f (which was backed out in 943f066c0d58), with an extra line removed to fix problems with hg serve. hg's internal web server contains checking if the app isn't trying to write more bytes than specified by the Content-Length header. The first try still contained an old line that wrote the response, so the response was sent twice.