This maintains the number of successive visits resulting in the same status.
For example, when the last 3 visits are successful evenful ones, this field value will
be 3. Then, an uneventful visit coming right after the latest eventful one will reset
this counter to 1 (last event is "uneventful" and only one such event happened
successively)...
This will help when implementing disabling of too many failed visit attempts on a given
origin.
Related to T2345
Depends on D5956
Supersedes D4895 (which I plan to commandeer and close)