The following is an excerption from the WL.
      
   1. Change so that MIXED is default format
      1.1 to change the default for command line --binlog-format
      1.2 to alter global_system_variables.binlog_format calculation
          basing on command line --binlog-format parameter and 
          its default.
   2. Change test suite so that more testing is done by MIXED format.
      2.1 to check if there are test cases requiring --binlog-foramt=statement via
          `source include/have_binlog_format_statement.inc' and affected by 
          altering the latter to be "mixed".
      2.2 to check the content of such vulnerable cases to find if
          extending to the mixed does not modify results. In that case simply
          substitute source arguments as explained.
      2.3 if a test in mixed mode deals with features triggering
          row-binlogging then if necessary we can switch explicitly
          to statement mode or create another test to run with 
          non-recommended STATEMENT mode
   
          Particullarily, extracting INSERT DELAYED 
          binlogging subtest for statement mode is performed, and 
          the snippet is moved into a separate test file.
          Note that since now all three modes verify this use case
          through 3 different tests.
   
   No changes in item 3 of HLD appeared to be needed.