[1293] update ZONEMGR_UNKNOWN_ZONE_FAIL description

src/bin/zonemgr/zonemgr_messages.mes

@@ -128,9 +128,11 @@ a bug report.
 
 % ZONEMGR_UNKNOWN_ZONE_FAIL zone %1 (class %2) is not known to the zone manager
 An XFRIN operation has failed but the zone that was the subject of the
-operation is not being managed by the zone manager.  This may indicate
-an error in the program (as the operation should not have been initiated
-if this were the case).  Please submit a bug report.
+operation is not being managed by the zone manager. This can be either the
+result of a bindctl command to transfer in a currently unknown (or mistyped)
+zone, or, if this error appears without the administrator giving transfer
+commands, it can indicate an error in the program, as it should not have
+initiated transfers of unknown zones on its own.
 
 % ZONEMGR_UNKNOWN_ZONE_NOTIFIED notified zone %1 (class %2) is not known to the zone manager
 A NOTIFY was received but the zone that was the subject of the operation