The value of 'xcmHrDevAlertIndex' for the most recently-added
critical alert in the alert table. This value only reflects the
most recently added alert; if the alert is subsequently cleared,
the value of 'xcmHrDevAlertLastCriticalAlertIndex' SHALL NOT be
changed as a result. Compliant implementations SHALL report
zero if no critical alerts have been added to the table.
A management tool may use the fact that this value has not
changed to avoid checking for new critical alerts.
Note that the value of this object will 'wrap' when the first
critical alert is added to the table after 'xcmHrDevAlertIndex'
has reached 2**32 - 1 and 'wrapped' to 1.