pycompat: import correct cookie module on Python 3

http.cookielib doesn't exist. http.cookiejar does and it contains the
symbols we need. This fixes test failures on Python 3.

mercurial/pycompat.py

@@ -25,7 +25,7 b' if not ispy3:'
     import SocketServer as socketserver
     import xmlrpclib
 else:
-    import http.cookielib as cookielib
+    import http.cookiejar as cookielib
     import http.client as httplib
     import pickle
     import queue as _queue