Use repo vfs to join the server log
The method join on repo has been removed in changeset edb7f628ef8b of
mercurial.
# Log every push and pull to the servelog
[hooks]
changegroup.aaaaa_servelog = python:mercurialserver.servelog.hook
outgoing.aaaaa_servelog = python:mercurialserver.servelog.hook
pushkey.aaaaa_servelog = python:mercurialserver.servelog.phaseshook