Outdated replication protocol error?

Commit 5ee2197767 (about 4 years old) introduced the error:

  "IDENTIFY_SYSTEM has not been run before START_REPLICATION"

But it seems like running START_REPLICATION first works (at least in
the simple case).

We should either:

1. Document that IDENTIFY_SYSTEM must always be run before
START_REPLICATION, and always issue a WARNING if that's not done (an
ERROR might break existing applications); or

2. If the commit is out of date and no longer needed, or if it's easy
enough to fix, just remove the error (and Assert a valid
ThisTimeLineID).

Regards,
    Jeff Davis