Bug #14188 BINARY variables have no 0x00 padding

Description:
Rule: "zero padding on insert". For any change of
a BINARY(n) target, e.g. INSERT or UPDATE or "SET
variable=value", if length(target) > length(source),
pad target with trailing 0x00 ('\0') bytes. It
does happen if the target is a column. It doesn't happen
if the target is a variable or parameter.

This test was originally mentioned in a comment for bug#9278.
Fix should be for 5.0 only.

How to repeat:
mysql> delimiter //
mysql> create procedure ph0 (p1 binary(2)) begin declare v1 binary(2)
default 0x41; select hex(p1),hex(v1); end//
Query OK, 0 rows affected (0.03 sec)

mysql> call ph0(0x41)//
+---------+---------+
| hex(p1) | hex(v1) |
+---------+---------+
| 41      | 41      |
+---------+---------+
1 row in set (0.01 sec)

Verified on 5.0.15 (ChangeSet@1.2022, 2005-10-20 11:12:34+05:00, bar@mysql.com) on Linux:

mysql> delimiter //
mysql> create procedure ph0 (p1 binary(2)) begin declare v1 binary(2)
    -> default 0x41; select hex(p1),hex(v1); end//
Query OK, 0 rows affected (0,02 sec)

mysql> call ph0(0x41)//
+---------+---------+
| hex(p1) | hex(v1) |
+---------+---------+
| 41      | 41      |
+---------+---------+
1 row in set (0,00 sec)

Query OK, 0 rows affected (0,00 sec)

mysql> create table tbi(c1 binary(2))//
Query OK, 0 rows affected (0,01 sec)

mysql> insert into tbi values (0x41)//
Query OK, 1 row affected (0,01 sec)

mysql> select hex(c1) from tbi//
+---------+
| hex(c1) |
+---------+
| 4100    |
+---------+
1 row in set (0,00 sec)

mysql> select version()//
+-----------+
| version() |
+-----------+
| 5.0.15    |
+-----------+
1 row in set (0,00 sec)

Noted in 5.0.18 changelog.