Problem: When an Incident_log_event contains a bad incident number on disk,
the server crashes with an assertion.
Fix: Don't validate input with assertions. Use errors.
Adding an event that can be used to denote that an incident occured
on the master. The event can be used to denote a gap in the replication
stream, but can also be used to denote other incidents.
In addition, the injector interface is extended with functions to
generate an incident event. The function will also rotate the binary
log after generating an incident event to get a fresh binary log.
