--disable_reconnect and --enable_reconnect to mysqltest
so that it can be tested properly. (Bug #8866)


client/mysqltest.c:
  Add support for --disable_reconnect and --enable_reconnect
mysql-test/r/kill.result:
  Update results
mysql-test/t/kill.test:
  Fix test to actually verify that killing a connection is working,
  and that automatic reconnect is working as desired.
sql-common/client.c:
  Clean up MYSQL->stmts on reconnect by invalidating statements
  not in the MYSQL_STMT_INIT_DONE state, and reconnecting others
  to the new MYSQL object.