hgweb: fix the MRO in Python 3

object should appear at the end, otherwise it tries to pre-empt the other
new-style classes in the MRO, resulting in an unresolvable MRO in Py3. We still
need to include object because otherwise in 2.7 we end up with an old-style
class if threading is not supported, new-style if it is.

mercurial/hgweb/server.py

@@ -263,7 +263,7 b' def openlog(opt, default):'
         return open(opt, 'a')
     return default
 
-class MercurialHTTPServer(object, _mixin, httpservermod.httpserver):
+class MercurialHTTPServer(_mixin, httpservermod.httpserver, object):
 
     # SO_REUSEADDR has broken semantics on windows
     if os.name == 'nt':