modified for MySQL 5.5. Logger service moved to the
        plugin/sql_errlog directory to be properly used later.

plugin/sql_errlog/sql_errlog.c:
  Fixes for bugs #956427 (SQL_ERROR_LOG plugin produces bogus warnings about sql-error-log-size-limit value) and #956463 (Server crashes if SQL_ERROR_LOG fails to initialize) they're also MDEV-184 and MDEV-183
    
  The sql_error_log_deinit() should be prepared for the logger_file to be NULL.
  The logger_file_size_limit upper limit wasn't properly set.