Bug #16857 Altering BINARY(x) column uses incorrect padding

Description:
Given a BINARY(X) column, using ALTER TABLE to change the column to BINARY(Y) where Y > X, the end of the column is padded with 0x20 instead of 0x00.

How to repeat:
create table table1 (col1 binary(4));
insert into table1 values ('a'),('a ');
select hex(col1) from table1;
alter table table1 modify col1 binary(10);
select hex(col1) from table1;
insert into table1 values ('b'),('b ');
select hex(col1) from table1;

mysql 5.0.19-debug (root) [test]> create table table1 (col1 binary(4));
Query OK, 0 rows affected (0.00 sec)

mysql 5.0.19-debug (root) [test]> insert into table1 values ('a'),('a ');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql 5.0.19-debug (root) [test]> select hex(col1) from table1;
+-----------+
| hex(col1) |
+-----------+
| 61000000  |
| 61200000  |
+-----------+
2 rows in set (0.00 sec)

mysql 5.0.19-debug (root) [test]> alter table table1 modify col1 binary(10);
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql 5.0.19-debug (root) [test]> select hex(col1) from table1;
+----------------------+
| hex(col1)            |
+----------------------+
| 61000000202020202020 |
| 61200000202020202020 |
+----------------------+
2 rows in set (0.00 sec)

mysql 5.0.19-debug (root) [test]> insert into table1 values ('b'),('b ');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql 5.0.19-debug (root) [test]> select hex(col1) from table1;
+----------------------+
| hex(col1)            |
+----------------------+
| 61000000202020202020 |
| 61200000202020202020 |
| 62000000000000000000 |
| 62200000000000000000 |
+----------------------+
4 rows in set (0.00 sec)

Suggested fix:
The server should use 0x00 instead of 0x20 to pad BINARY columns when they are altered to a larger size.

Verified w/fresh pull of 5.0 under FC4

Leads to data corruption.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/3410

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/3411

BINARY columns should not be treated as other *CHAR columns when it comes to expanding columns.  Changeset 1.2096, in v5.0.19 changes the behavior to fill new positions in expanded BINARY columns with 0x00 bytes instead of ASCII spaces.

Noted in 5.0.19 changelog.

Using <literal>ALTER TABLE</literal> to increase the length of
a <literal>BINARY(<replaceable>M</replaceable>)</literal>
column caused column values to be padded with spaces rather
than <literal>0x00</literal> bytes. (Bug #16857)

Noted in 5.1.8 changelog, too.