repository (incredible that I forgot to push, but why not).
So unfortunately the bugfix missed 3.23.57 and will be in .58 :(
Instead of looking like working (bug #198), replication between
a 3.23 slave and 4.0 master should frankly stop. Here we detect
4.0 masters in the 3.23 slave code when we see a strange Rotate
event, and in that case we print an error and stop.
4.0.13 and older masters will be "often" caught (see the patch); 4.0.14
and newer masters will always be immediately caught.


sql/slave.cc:
  Instead of looking like working (bug #198), replication between
  a 3.23 slave and 4.0 master should frankly stop. Here we detect
  4.0 masters in the 3.23 slave code when we see a strange Rotate
  event, and in that case we print an error and stop.
  4.0.13 and older masters will be "often" caught (see the patch); 4.0.14
  and newer masters will always be immediately caught.