MDEV-18237 InnoDB: Unable to drop FTS index aux table and further errors (possibly bogus)

row_drop_table_for_mysql(): Fix a regression introduced in MDEV-16515.
Similar to the follow-up fixes MDEV-16647 and MDEV-17470, we must make
the internal tables of FULLTEXT INDEX immune to kills, to avoid noise
and resource leakage on DROP TABLE or ALTER TABLE. (Orphan internal tables
would be dropped at the next InnoDB startup only.)

storage/innobase/row/row0mysql.cc

 /*****************************************************************************
 
 Copyright (c) 2000, 2018, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2015, 2018, MariaDB Corporation.
+Copyright (c) 2015, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -4225,7 +4225,9 @@ row_drop_table_for_mysql(
 		hold the InnoDB dictionary lock, we will drop any
 		adaptive hash index entries upfront. */
 		const bool is_temp = dict_table_is_temporary(table)
-			|| strstr(tablename_minus_db, tmp_file_prefix);
+			|| strncmp(tablename_minus_db, tmp_file_prefix,
+				   tmp_file_prefix_length)
+			|| strncmp(tablename_minus_db, "FTS_", 4);
 		while (buf_LRU_drop_page_hash_for_tablespace(table)) {
 			if ((!is_temp && trx_is_interrupted(trx))
 			    || srv_shutdown_state != SRV_SHUTDOWN_NONE) {

storage/xtradb/row/row0mysql.cc

 /*****************************************************************************
 
 Copyright (c) 2000, 2018, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2015, 2018, MariaDB Corporation.
+Copyright (c) 2015, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -4235,7 +4235,9 @@ row_drop_table_for_mysql(
 		hold the InnoDB dictionary lock, we will drop any
 		adaptive hash index entries upfront. */
 		const bool is_temp = dict_table_is_temporary(table)
-			|| strstr(tablename_minus_db, tmp_file_prefix);
+			|| strncmp(tablename_minus_db, tmp_file_prefix,
+				   tmp_file_prefix_length)
+			|| strncmp(tablename_minus_db, "FTS_", 4);
 		while (buf_LRU_drop_page_hash_for_tablespace(table)) {
 			if ((!is_temp && trx_is_interrupted(trx))
 			    || srv_shutdown_state != SRV_SHUTDOWN_NONE) {