bug#10952

"alter table from MyISAM to MERGE lost data without errors and warnings"
  Add new handlerton flag which prevent user from altering table storage
  engine to storage engines which would lose data. Both 'blackhole' and 
  'merge' are marked with the new flag.
  Tests included.

sql/handler.h

@@ -408,6 +408,7 @@ struct show_table_alias_st {
 #define HTON_ALTER_NOT_SUPPORTED     (1 << 1) //Engine does not support alter
 #define HTON_CAN_RECREATE            (1 << 2) //Delete all is used fro truncate
 #define HTON_HIDDEN                  (1 << 3) //Engine does not appear in lists
+#define HTON_ALTER_CANNOT_CREATE     (1 << 4) //Cannot use alter to create
 
 typedef struct st_thd_trans
 {