Bug #42451 setup_fake_relay_log makes an incorrect path on windows

Path composition for the relay log file that is stored into the relay index
file was not correct for windows.
mysql-test language does not provide primitives for portable path composition.
      
Fixed with storing only the basename part of the external "fake" relay log into
the relay index file.
Safety of removal of the dirname part of the relaylog is provided by logics of
`setup_fake_relay_log' that places the fake file into @@datadir directory.


mysql-test/include/setup_fake_relay_log.inc:
  storing only the basename part of the external "fake" relay log into the relay
  log index.
mysql-test/suite/rpl/t/rpl_cross_version.test:
  restoring test for windows.

mysql-test/include/setup_fake_relay_log.inc

@@ -69,9 +69,9 @@ let $_fake_relay_log_purge= `SELECT @@global.relay_log_purge`;
 # Create relay log file.
 copy_file $fake_relay_log $_fake_relay_log;
 # Create relay log index.
---exec echo $_fake_relay_log > $_fake_relay_index
+--exec echo $_fake_filename-fake.000001 > $_fake_relay_index
 
 # Setup replication from existing relay log.
-eval CHANGE MASTER TO MASTER_HOST='dummy.localdomain', RELAY_LOG_FILE='$_fake_relay_log', RELAY_LOG_POS=4;
+eval CHANGE MASTER TO MASTER_HOST='dummy.localdomain', RELAY_LOG_FILE='$_fake_filename-fake.000001', RELAY_LOG_POS=4;
 
 --enable_query_log

mysql-test/suite/rpl/t/rpl_cross_version.test

@@ -11,7 +11,7 @@
 #
 
 --source include/have_log_bin.inc
---source include/not_windows.inc
+
 #
 # Bug#31240 load data infile replication between (4.0 or 4.1) and 5.1 fails
 #