BUG#22708 - Error message doesn't refer to storage engine unsupported

When openning a table with unsupported (disabled or not compiled)
storage engine, confusing error message is returned.

Return better error message when we're attempting to open a table
that uses unsupported engine.

mysql-test/r/bdb_notembedded.result

+set autocommit=1;
+reset master;
+create table bug16206 (a int);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+show binlog events;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+f	n	Format_desc	1	n	Server ver: VERSION, Binlog ver: 4
+f	n	Query	1	n	use `test`; create table bug16206 (a int)
+f	n	Query	1	n	use `test`; insert into bug16206 values(1)
+f	n	Query	1	n	use `test`; insert into bug16206 values(2)
+drop table bug16206;
+reset master;
+create table bug16206 (a int) engine=         bdb;
+insert into bug16206 values(0);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+insert into bug16206 values(3);
+show binlog events;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+f	n	Format_desc	1	n	Server ver: VERSION, Binlog ver: 4
+f	n	Query	1	n	use `test`; create table bug16206 (a int) engine=         bdb
+f	n	Query	1	n	use `test`; insert into bug16206 values(0)
+f	n	Query	1	n	use `test`; insert into bug16206 values(1)
+f	n	Query	1	n	use `test`; BEGIN
+f	n	Query	1	n	use `test`; insert into bug16206 values(2)
+f	n	Query	1	n	use `test`; COMMIT
+f	n	Query	1	n	use `test`; insert into bug16206 values(3)
+drop table bug16206;
+set autocommit=0;
+End of 5.0 tests

mysql-test/t/bdb_notembedded.test

+-- source include/not_embedded.inc
+-- source include/have_bdb.inc
+
+#
+# Bug #16206: Superfluous COMMIT event in binlog when updating BDB in autocommit mode
+#
+set autocommit=1;
+
+let $VERSION=`select version()`;
+
+reset master;
+create table bug16206 (a int);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+--replace_result $VERSION VERSION
+--replace_column 1 f 2 n 5 n
+show binlog events;
+drop table bug16206;
+
+reset master;
+create table bug16206 (a int) engine=         bdb;
+insert into bug16206 values(0);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+insert into bug16206 values(3);
+--replace_result $VERSION VERSION
+--replace_column 1 f 2 n 5 n
+show binlog events;
+drop table bug16206;
+
+set autocommit=0;
+
+
+--echo End of 5.0 tests

sql/table.cc

@@ -886,26 +886,31 @@ static int open_binary_frm(THD *thd, TABLE_SHARE *share, uchar *head,
                             ha_legacy_type(share->db_type())));
       }
 #ifdef WITH_PARTITION_STORAGE_ENGINE
-      else
+      else if (str_db_type_length == 9 &&
+               !strncmp((char *) next_chunk + 2, "partition", 9))
       {
-        LEX_STRING pname= { C_STRING_WITH_LEN( "partition" ) };
-        if (str_db_type_length == pname.length &&
-            !strncmp((char *) next_chunk + 2, pname.str, pname.length))
-        {
-          /*
-            Use partition handler
-            tmp_plugin is locked with a local lock.
-            we unlock the old value of share->db_plugin before
-            replacing it with a globally locked version of tmp_plugin
-          */
-          plugin_unlock(NULL, share->db_plugin);
-          share->db_plugin= ha_lock_engine(NULL, partition_hton);
-          DBUG_PRINT("info", ("setting dbtype to '%.*s' (%d)",
-                              str_db_type_length, next_chunk + 2,
-                              ha_legacy_type(share->db_type())));
-        }
+        /*
+          Use partition handler
+          tmp_plugin is locked with a local lock.
+          we unlock the old value of share->db_plugin before
+          replacing it with a globally locked version of tmp_plugin
+        */
+        plugin_unlock(NULL, share->db_plugin);
+        share->db_plugin= ha_lock_engine(NULL, partition_hton);
+        DBUG_PRINT("info", ("setting dbtype to '%.*s' (%d)",
+                            str_db_type_length, next_chunk + 2,
+                            ha_legacy_type(share->db_type())));
       }
 #endif
+      else if (!tmp_plugin)
+      {
+        /* purecov: begin inspected */
+        error= 8;
+        my_error(ER_UNKNOWN_STORAGE_ENGINE, MYF(0), name.str);
+        my_free(buff, MYF(0));
+        goto err;
+        /* purecov: end */
+      }
       next_chunk+= str_db_type_length + 2;
     }
     if (next_chunk + 5 < buff_end)
@@ -2188,6 +2193,8 @@ void open_table_error(TABLE_SHARE *share, int error, int db_errno, int errarg)
                     "of MySQL and cannot be read", 
                     MYF(0), buff);
     break;
+  case 8:
+    break;
   default:				/* Better wrong error than none */
   case 4:
     strxmov(buff, share->normalized_path.str, reg_ext, NullS);