Overriding a default value of --secure-file-priv on pb.mtr to be $MYSQLTEST_VARDIR which 
makes pb's mtr happy to execute the regression test for the bug.

Overriding a default value of --secure-file-priv on pb.mtr with a value allowable 
the test to pass on pb.

It's a regression issue.
The reason of the bug appeared to be an error introduced into 5.1 source code.
A piece of code in Create_file_log_event::do_apply_event() did not have test
coverage which made make test and pb unaware.
      
Fixed with inverting the old value of the return value from 
Create_file_log_event::do_apply_event().
The rpl test suite is extended with `rpl_cross_version' the file to hold 
regression cases similar to the current.

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.