py3: convert HTTP request headers to str The low-level request object ideally takes system strings for HTTP request headers and values. If we send in bytes, it works. But a duplicate header check fails and various tests emit duplicate user-agent headers. Differential Revision: https://phab.mercurial-scm.org/D4834

py3: use system strings in HTTP server code Previously the source transformer was converting some string literals to bytes and we were comparing a system native string to bytes and this was leading to sending the wrong HTTP response headers on Python 3. After this change, we now properly send Transfer-Encoding and Connection response headers on Python 3. Differential Revision: https://phab.mercurial-scm.org/D4833