mysql-test-run --core-file changed to --exit-info=256

                it's yet another mysqld hidden feature
                --exit-info=256 is like --core-file but prints info at exit.
                --exit-info itself implies also one-thread (undocumented)

mysql-test/mysql-test-run

@@ -321,7 +321,7 @@ start_master()
     	    --server-id=1 \
             --basedir=$MY_BASEDIR \
 	    --port=$MASTER_MYPORT \
-	    --core-file \
+	    --exit-info=256 \
             --datadir=$MASTER_MYDDIR \
 	    --pid-file=$MASTER_MYPID \
 	    --socket=$MASTER_MYSOCK \
@@ -347,7 +347,8 @@ start_slave()
 	    --master-connect-retry=1 \
 	    --master-host=127.0.0.1 \
 	    --master-port=$MASTER_MYPORT \
-	    --core-file --log-bin --log-slave-updates \
+	    --exit-info=256 \
+	    --log-bin --log-slave-updates \
             --basedir=$MY_BASEDIR \
             --datadir=$SLAVE_MYDDIR \
 	    --pid-file=$SLAVE_MYPID \