MDEV-4466 Partitioned Aria table created by a previous version is recognized as TEST_SQL_DISCOVERY

Partitioning didn't store the name of default storage engine for partitions
in the frm file - it only store the typecode. Typecodes aren't stable, and
might vary depending on the order in which storage engines are loaded (can
be changed even from my.cnf without recompilation).

As a temporary workaround for 5.5, we hard-code Aria's typecode, to make sure it
never changes.

sql/handler.h

@@ -356,7 +356,8 @@ enum legacy_db_type
   DB_TYPE_MARIA,
   /** Performance schema engine. */
   DB_TYPE_PERFORMANCE_SCHEMA,
-  DB_TYPE_FIRST_DYNAMIC=42,
+  DB_TYPE_ARIA=42,
+  DB_TYPE_FIRST_DYNAMIC=43,
   DB_TYPE_DEFAULT=127 // Must be last
 };
 /*

sql/table.cc

@@ -802,6 +802,11 @@ static int open_binary_frm(THD *thd, TABLE_SHARE *share, uchar *head,
     share->frm_version= FRM_VER_TRUE_VARCHAR;
 
 #ifdef WITH_PARTITION_STORAGE_ENGINE
+  /*
+    Yuck! Double-bad. Doesn't work with dynamic engine codes.
+    And doesn't lock the plugin. Fixed in 10.0.4
+  */
+  compile_time_assert(MYSQL_VERSION_ID < 100000);
   if (*(head+61) &&
       !(share->default_part_db_type= 
         ha_checktype(thd, (enum legacy_db_type) (uint) *(head+61), 1, 0)))

storage/maria/ha_maria.cc

@@ -3471,7 +3471,7 @@ static int ha_maria_init(void *p)
 
   maria_hton= (handlerton *)p;
   maria_hton->state= SHOW_OPTION_YES;
-  maria_hton->db_type= DB_TYPE_UNKNOWN;
+  maria_hton->db_type= DB_TYPE_ARIA;
   maria_hton->create= maria_create_handler;
   maria_hton->panic= maria_hton_panic;
   maria_hton->commit= maria_commit;