Changed last_insert_id() to be unsigned.

Fixed MDEV-331: last_insert_id() returns a signed number

mysql-test/r/auto_increment.result:
  Added test case
mysql-test/t/auto_increment.test:
  Added test case
sql/item_func.h:
  Changed last_insert_id() to be unsigned.

mysql-test/r/auto_increment.result

@@ -516,3 +516,25 @@ pk
 1
 18446744073709551614
 DROP TABLE t1;
+CREATE TABLE t1 (pk BIGINT UNSIGNED AUTO_INCREMENT, PRIMARY KEY (pk));
+insert into t1 values((1<<63)+1);
+insert into t1 values(null);
+select last_insert_id();
+last_insert_id()
+9223372036854775810
+select * from t1;
+pk
+9223372036854775809
+9223372036854775810
+drop table t1;
+CREATE TABLE t1 (pk BIGINT AUTO_INCREMENT, PRIMARY KEY (pk));
+insert into t1 values(-5);
+insert into t1 values(null);
+select last_insert_id();
+last_insert_id()
+1
+select * from t1;
+pk
+-5
+1
+drop table t1;

mysql-test/t/auto_increment.test

@@ -380,3 +380,19 @@ CREATE TABLE t1 (pk BIGINT UNSIGNED AUTO_INCREMENT, PRIMARY KEY (pk));
 INSERT INTO t1 VALUES (NULL), (18446744073709551615-1), (NULL);
 SELECT * FROM t1;
 DROP TABLE t1;
+
+# MDEV-331 last_insert_id() returns a signed number
+# Check that last_insert_id() generates a signed value
+CREATE TABLE t1 (pk BIGINT UNSIGNED AUTO_INCREMENT, PRIMARY KEY (pk));
+insert into t1 values((1<<63)+1);
+insert into t1 values(null);
+select last_insert_id();
+select * from t1;
+drop table t1;
+
+CREATE TABLE t1 (pk BIGINT AUTO_INCREMENT, PRIMARY KEY (pk));
+insert into t1 values(-5);
+insert into t1 values(null);
+select last_insert_id();
+select * from t1;
+drop table t1;

sql/item_func.h

@@ -1201,6 +1201,7 @@ public:
   {
     if (arg_count)
       max_length= args[0]->max_length;
+    unsigned_flag=1;
   }
   bool fix_fields(THD *thd, Item **ref);
   bool check_vcol_func_processor(uchar *int_arg)