mysql-test/r/mysqld--help-notwin.result:
  consequence of introducing opt_autocommit and its default
mysql-test/suite/sys_vars/r/autocommit_func4.result:
  Before this fix, this test would have shown @@global.autocommit == 0
  in spite of --autocommit=on.
mysql-test/suite/sys_vars/r/autocommit_func5.result:
  result unchanged by the fix
sql/mysqld.cc:
  atoi(argument) was reliable for =0|1 parameters. Now that boolean options
  must support =on/off/true/false, atoi(argument) is wrong (being always 0
  for those strings). Instead, let the internal logic of my_getopt
  (in particular get_bool_argument()) set a boolean opt_autocommit
  properly, and use that to set global_system_variables.option_bits.