Give proper error to client on shutdown.

configure.in:
  Increased version number
mysql-test/mysql-test-run.pl:
  Ignore errors that one can get while running with --mysqld=--log-warnings=2
mysql-test/r/variables.result:
  Remember original value of log_warnings
mysql-test/suite/rpl/r/rpl_idempotency.result:
  Ignore errors that one can get while running with --mysqld=--log-warnings=2
mysql-test/suite/rpl/t/rpl_idempotency.test:
  Ignore errors that one can get while running with --mysqld=--log-warnings=2
mysql-test/t/variables.test:
  Remember original value of log_warnings
sql/mysqld.cc:
  Give proper error to close_connection() on shutdown
storage/maria/ha_maria.cc:
  Added missing DBUG_RETURN