MDEV-4786 - merge 10.0-monty - 10.0

Fixed main.plugin, main-test_sql_discovery.plugin failures.

storage/example/ha_example.cc:
  Issue a warning independently of DBUG status (needed for testing).

storage/example/ha_example.cc

@@ -964,7 +964,6 @@ bool ha_example::check_if_incompatible_data(HA_CREATE_INFO *info,
     DBUG_RETURN(COMPATIBLE_DATA_NO);
   }
 
-#ifndef DBUG_OFF
   for (uint i= 0; i < table->s->fields; i++)
   {
     ha_field_option_struct *f_old, *f_new;
@@ -982,7 +981,6 @@ bool ha_example::check_if_incompatible_data(HA_CREATE_INFO *info,
     else
       DBUG_PRINT("info", ("old field %i did not changed", i));
   }
-#endif
 
   DBUG_RETURN(COMPATIBLE_DATA_YES);
 }