Implementation of MDEV-28 LIMIT ROWS EXAMINED

https://mariadb.atlassian.net/browse/MDEV-28
  
This task implements a new clause LIMIT ROWS EXAMINED <num>
as an extention to the ANSI LIMIT clause. This extension
allows to limit the number of rows and/or keys a query
would access (read and/or write) during query execution.

sql/sql_insert.cc

@@ -3280,6 +3280,8 @@ int select_insert::send_data(List<Item> &values)
     unit->offset_limit_cnt--;
     DBUG_RETURN(0);
   }
+  if (thd->killed == ABORT_QUERY)
+    DBUG_RETURN(0);
 
   thd->count_cuted_fields= CHECK_FIELD_WARN;	// Calculate cuted fields
   store_values(values);