mysql-test/r/no-threads.result:
  Test that we are in the 'no-threads' thread_handling mode.
mysql-test/t/no-threads.test:
  Test that we are in the 'no-threads' thread_handling mode.
sql/mysqld.cc:
  Changes to make global_system_variables.thread_handling be zero based, instead of 1
  based.
sql/scheduler.h:
  Changed the enum to start at 0, to match the array elements in thread_handling_names
  in mysqld.cc