Fix for Mac OS X shutdown


mysql-test/mysql-test-run.sh:
  Log client error messages
mysql-test/r/null_key.result:
  Test for bug in <=> NULL
mysql-test/t/null_key.test:
  Test for bug in <=> NULL
sql/mysqld.cc:
  Fix for Mac OS X shutdown
sql/opt_range.cc:
  Fixed bug with indexed NULL column <=> NULL