The 'slave_patternload_file' is assigned to the real path of the load data file 
when initializing the object of Relay_log_info. But the path of the load data
file is not formatted to real path when executing event from relay log. So the 
error will be encountered if the path of the load data file is a symbolic link.

Actually the global 'opt_secure_file_priv' is not formatted to real path when 
loading data from file. So the same thing will happen too.

      
To fix these errors, the path of the load data file should be formatted to 
real path when executing event from relay log. And the 'opt_secure_file_priv' 
should be formatted to real path when loading data infile.