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.
Fixing pb failures caused by mtr invokes the test with --tmpdir to which
there are sensitive operations in the test
and setup_fake_relay_log.inc also needed --secure-file-priv for its own separate
directory.
Fixed with removing SELECT INTO OUTFILE and deploying --exec echo instead in the marco.
The test's opt file should contain --secure-file-priv=$MYSQL_TEST_DIR as the test
operations deal with files located in $MYSQL_TEST_DIR.
Problem: When an Incident_log_event contains a bad incident number on disk,
the server crashes with an assertion.
Fix: Don't validate input with assertions. Use errors.
