hgweb: pre-init mimetypes module (fixes ugly bug in python-2.6.2 mimetypes)

The ugly initialization hack in mimetypes' initialization procedure can make
hg serve hit the maximum recursion depth when in threaded mode.

mercurial/hgweb/server.py

@@ -283,6 +283,9 b' def create_server(ui, repo):'
     else:
         handler = _hgwebhandler
 
+    # ugly hack due to python issue5853 (for threaded use)
+    import mimetypes; mimetypes.init()
+
     try:
         if use_ipv6:
             return IPv6HTTPServer((address, port), handler)